CAMEL is invited by and will demonstrate two CXL platforms at the CXL Forum 2022


CAMEL team is invited to demonstrate two hot topics about CXL memory disaggregation and storage pooling at CXL Forum 2022, which is the hottest session at Flash Memory Summit (led by the CXL Consortium and MemVerge). That deals with CXL updates from the CXL Consortium, Korea Advanced Institute of Science and Technology (KAIST), ARM, Astera Labs,, Hazelcast, Kioxia, Lenovo, Montage, NGD Systems, PhoenixNAP, Rambus, Smart Modular, Synopsys, University of Michigan TPP team, and Xconn. Our sessions will start on August 2nd, 4:40PM PT.

In the first session, entitled "CXL-SSD: Expanding PCIe Storage as Working Memory over CXL", we will argue that CXL is helpful in leveraging PCIe-based block storage to incarnate a large, scalable working memory. CXL could be a cost-effective, and practical interconnect technology that can bridge PCIe storage’s block semantics to memory-compatible byte semantics. To this end, we should carefully integrate the block storage into its interconnect network by being aware of the diversity of device types and protocols that CXL supports. This talk first discusses what mechanism makes the PCIe storage impractical and unable to be used for a memory expander. Then, it will explore all the CXL device types and their protocol interfaces to answer which configuration would be the best for the PCIe storage to expand the host’s CPU memory. In the second session, we will demonstrate our CXL 2.0 end-to-end system, including the CXL network and memory expanders. You can check more detailed information about who will be in the CXL forum and how to register to attend via Zoom through the given below link.

Check more: [ Full Program ] [ Register ]

Miryeong won the NVMW memorable paper award this year!


Our team (Miryeong, Donghyung, Sangwon -- Miryeong is the first author) has won the Memorable Paper Award from NVMW 2022 for their paper "HolisticGNN: Geometric Deep Learning Engines for Computational SSDs". This work deals with in-storage processing for large-scale GNN (graph neural network) using a novel computational SSD (CSSD) architecture and machine learning framework. Basically, it performs preprocessing of GNN in storage like near data processing (including sampling, graph conversion, etc.) and accelerates inference procedures over reconfigurable hardware. The team fabricates HolisticGNN’s hardware RTL and implements its software on an FPGA-based CSSD as well.

The NVMW memorable paper award is one of the prestige awards in non-volatile memory areas. It selects two papers published in the past two years in TOP-TIER venues and journals such as OSDI, SOSP, FAST, ISCA, MICRO, ASPLOS, and ATC. Among them, NVMW committee members not only examine the quality of all the top venue papers and corresponding presentations but also check the significant impact on non-volatile memory research fields. NVMW (founded in 2010) is a non-volatile memory workshop held annually by the Center for Memory and Recording Research (CMRR) and Non-Volatile Systems Laboratory (NVSL). For the past 13 years, there have been nine NVMW memorable paper awards. Miryeong's HolisticGNN work takes the top among all the candidates this year, and it is the first award that KAIST has achieved. She also got $1000 cash prize. Congratulations! You can check the history of all past winners here all the memorable paper award winners.

Our CXL 2.0-based Memory Expander and End-to-End System are introduced by the Next Platform’s headline


The hyperscalers and cloud builders are not the only ones having fun with the CXL protocol and its ability to create tiered, disaggregated, and composable main memory for systems. HPC centers are getting in on the action, too, and in this case, the nextplatform is specifically talking about the Korea Advanced Institute of Science and Technology.

Researchers at KAIST’s CAMELab have joined the ranks of Meta Platforms (Facebook), with its Transparent Page Placement protocol and Chameleon memory tracking, and Microsoft with its zNUMA memory project, is creating actual hardware and software to do memory disaggregation and composition using the CXL 2.0 protocol atop the PCI-Express bus and a PCI-Express switching complex in what amounts to a memory server that it calls DirectCXL. The DirectCXL proof of concept was talked about it in a paper that was presented at the USENIX Annual Technical Conference last week, in a brochure that you can browse through here, and in a short video. (This sure looks like startup potential to the nextplatform .) -- Timothy Prickett Morgan

Read more: [ Headline ]

We have four studies that will be demonstrated at Hot series venues (HotChips and HotStorage)


We have four research works that have been accepted from HotStorage’22 and HotChips34. The topics that our study deal with include i) CXL-enabled storage-integrated memory expanders (CXL-SSD), ii) an advanced system stack for high-performance ZNS, iii) a scalable RAID system for next-generation storage, and iv) large-scale GNN services through computational SSD and in-storage processing architecture. The works have been done by Miryeong Kwon, Donghyun Gouk, Hanyeoreum Bae, and Jiseon Kim. Congratulation! We are excited to see you all at HotStorage and HotChips this year! Please see the detail in our publication list [Publications]. The corresponding papers and slides will be updated soon.

Donghyun and Sangwoon's memory pooling with compute express link (CXL) has been accepted from USENIX ATC'22


New cache coherent interconnects such as CXL have recently being attracted great attention thanks to their excellent capabilities of hardware heterogeneity management and resource disaggregation. Even though there is yet no real product or platform integrating CXL into memory disaggregation, it is expected to make memory resources practically and efficiently disaggregated much better than ever before.

In this paper, we propose direct accessible memory disaggregation, DirectCXL that directly connects a host processor complex and remote memory resources over CXL’s memory protocol (CXL.mem). To this end, we explore several practical designs for CXL-based memory disaggregation and make them real. As there is no operating system that supports CXL, we also offer CXL software runtime that allows users to utilize the underlying disaggregated memory resources via sheer load/store instructions. Since DirectCXL does not require any data copies between the host memory and remote memory, it can expose the true performance of remote-side disaggregated memory resources to the users. This year, the acceptance rate of USENIX ATC is 16%. Congratulations!!

Miryeong and Seungjoon KVS SSDs with strong latency determinism has been accepted from USENIX ATC'22


We propose Vigil-KV, a hardware and software co-designed framework that eliminates long-tail latency almost perfectly by introducing strong latency determinism. To make Get latency deterministic, Vigil-KV first enables a predictable latency mode (PLM) interface on a real datacenter-scale NVMe SSD, being aware of the nature of the underlying flash technologies. Vigil-KV at the system-level then hides the non-deterministic time window (being associated with SSD internal tasks and/or write services) by internally scheduling the different device states of PLM across multiple physical functions. Vigil-KV further schedules compaction/flush operations and client requests being aware of PLM's restrictions thereby integrating strong latency determinism into LSM KVs. We implement Vigil-KV upon a 1.92TB NVMe SSD prototype and Linux 4.19.91, but other LSM KVs can adopt its concept. We evaluate diverse Facebook and Yahoo scenarios with Vigil-KV, and our evaluation shows that Vigil-KV can reduce the tail latency of a baseline KV system by 3.19x while reducing the average latency by 34%, on average.

This year, the acceptance rate of USENIX ATC is 16%. Congratulations!!

CAMEL's Large-Scale Computatioanl SSD Research Has Been Awarded from IITP


CAMEL’s computational SSD research project is just awarded by the Institute of Information & Communications Technology Planning & Evaluation (IITP). The research will expose the practical but fundamental limits of the computational storage model, including the concept of Near-Data Processing (NDP), Smart SSD, and in-storage processing (ISP), and explore why computational SSDs have not been adopted in the industry by far. The research project will also suggest a breaking-through model and solutions that make computational SSDs be deployed in many computation domains ranging from enterprise-scale to cloud computing to data-centers.

This project includes the development of actual storage cards, hardware RTL, firmware, and large-scale I/O-centric operating systems, enabling a new model of generic computational SSDs. $5M (USD) solely coming from IITP will in total support CAMEL’s intelligent flash and computational storage projects for the next three years.

CAMEL uncovers The World-first CXL-based Memory Disaggregation IPs


As the big data era arrives, resource disaggregation has attracted significant attention thanks to its excellent scale-out capability, cost efficiency, and transparent elasticity. Disaggregating processors and storage devices well does break the physical boundaries of data centers and high-performance computing into separate physical entities. In contrast to the other resources, it is non-trivial to achieve a memory disaggregation technique that supports high performance and scalability with low cost. Many industry prototypes and academic simulation/emulation-based studies explore a wide spectrum of approaches to realize such memory disaggregation technology and put significant efforts into making memory disaggregation practical. However, the concept of memory disaggregation has not been successfully realized by far due to several fundamental challenges.

CAMEL has prototyped the world-first CXL solution (POC) that directly connects a host processor complex and remote memory resources over computing express link (CXL) protocol. CAMEL’s solution framework includes a set of CXL hardware and software IPs, including CXL switch, processor complex IP, and CXL memory controller. The solution framework can completely decouple memory resources from computing resources and enable high-performance, fully scale-out memory disaggregation architecture.

Read more: [ White paper ]

Our Hardware and Software Co-Design for Energy-Efficient Full System Persistence is accepted by ISCA'22


LightPC work argues that there is a better way to use PRAM than what Intel's Optane Persistent Memory solution uses. We implement a real persistent system and OS, which put all pure NVM DIMMs, NVM controllers, and RISC-V-based 03 octa-core CPU altogether. LightPC has NO volatile states at the runtime (e.g., DRAM) and guarantees that the target system doesn't lose any multi-threaded program execution, data in the heal and stack. In addition, you don't need to change anything on your application

ABSTRACT: We propose LightPC, a lightweight persistence-centric platform to make the system robust against power loss. LightPC consists of hardware and software subsystems, each being referred to as open-channel PMEM (OC-PMEM) and persistence-centric OS (PecOS). OC-PMEM removes physical and logical boundaries in drawing a line between volatile and non-volatile data structures by unshackling new memory media from conventional PMEM complex. PecOS provides a single execution persistence cut to quickly convert the execution states to persistent information in cases of a power failure, which can eliminate persistent control overhead. We prototype LightPC's computing complex and OC-PMEM using our custom system board. PecOS is implemented based on Linux 4.19 and Berkeley bootloader on the hardware prototype. Our evaluation results show that OC-PMEM can make user-level performance comparable with a DRAM only non-persistent system, while consuming 72% lower power and 69% less energy. LightPC also shortens the execution time of diverse HPC, SPEC and In-memory DB workloads, compared to traditional persistent systems by 1.6x and 8.8x, on average, respectively.

Our Hardware/Software Co-Programmable Framework for Computational SSDs to Accelerate GNNs is accepted by FAST'22


Graph neural networks (GNNs) process large-scale graphs that consist of a hundred of billion edges. In contrast to traditional deep learnings, the unique behaviors of GNNs are engaged with a large set of graph and embedding data on storage, which exhibits complex and irregular preprocessing.

We propose a novel deep learning framework on large graphs, HolisticGNN that provides easy-to-use, near-storage inference infrastructure for fast, energy efficient GNN processing. To achieve the best end-to-end latency and high energy efficiency, HolisticGNN allows users to implement various GNN algorithms where the actual data exist and executes them directly from near storage in a holistic manner. It also enables RPC over PCIe such that the users can simply program GNNs through a graph semantic library without understanding the underlying hardware or storage configurations at all. We fabricate HolisticGNN's hardware RTL and implement its software on our FPGA-based computational SSD (CSSD). Our empirical evaluations show that the inference time of HolisticGNN outperforms GNN inference services using high-performance modern GPUs by 7.1× while reducing energy consumption by 33.2×, on average. This year, the acceptance rate of fast is 21%. For the entire history of KAIST, there are only three papers published by USENIX FAST, and we have all of them!! Congratulations!

Read more: [ News at KAIST ] [ Naver headline + 26 ] [ Press/Newspaper ]

Our PMEM-based in-memory graph study has been accepted from ICCD'21


In this work, we investigate runtime environment characteristics and explore the challenges of existing in-memory graph processing. This system-level analysis includes results and observations, which are not reported in the literature with existing expectations of graph application users. To address a lack of memory space problem for big-scale graph analysis, we configure real persistent memory devices (PMEMs) with different operation modes and system software frameworks. Specifically, we introduce PMEM to a representative in-memory graph system, Ligra, and perform an in-depth analysis that uncovers the performance behaviors of different PMEM-applied in-memory graph systems. Based on the results, we also modify Ligra to improve the graph processing performance and data persistency. Our evaluation results reveal that Ligra, with our simple modification, exhibits 4.41× and 3.01× better performance than the original Ligra running on a virtual memory extension and conventional persistent memory.

Jie's optical network-based new memory for GPU has been accepted from MICRO'21


Traditional graphics processing units (GPUs) suffer from the low memory capacity and demand for high memory bandwidth. To address these challenges, we propose Ohm-GPU, a new optical network based heterogeneous memory design for GPUs. Specifically, Ohm-GPU can expand the memory capacity by combing a set of high-density 3D XPoint and DRAM modules as heterogeneous memory. To prevent memory channels from throttling throughput of GPU memory system, Ohm-GPU replaces the electrical lanes in the traditional memory channel with a high-performance optical network. However, the hybrid memory can introduce frequent data migrations between DRAM and 3D XPoint, which can occupy the memory channel and increase the optical network traffic. To prevent the intensive data migrations from blocking normal memory services, Ohm-GPU revises the existing memory controller and designs a new optical network infrastructure, which enables the memory channel to serve the data migrations and memory requests, in parallel. Our evaluation results reveal that Ohm-GPU can improve the performance by 181% and 27%, compared to a DRAM-based GPU memory system and the baseline optical network based heterogeneous memory system, respectively. This year, the acceptance rate of MICRO is 22%. Congratulations!

Prof. Jung will discuss new memory technologies for HPC at ISC'21 Invited Program


We will demonstrate novel applications that can be realized with emerging new memory technologies in high-performance computing and supercomputing systems at ISC'21 invited program. John Shalf who is the department of the head at Lawrence Berkeley National Laboratory will host Prof. Jung, Dr. Myung-Hee Na (the Vice President of SK Hynix), and Bruce Jacob (Keystone Professor of Electrical and Computer Engineering University of Maryland), and all we discuss the following issues: Non-volatile memory technologies are rapidly supplanting disk and tape. Furthermore, as NV memory performance is starting to match that of conventional volatile memory technologies, will the distinction between "storage" and "memory" starts to break down for future HPC and datacenter architectures? The panelists present a forward-looking vision for memory technologies (your choice of volatile or non-volatile or both) that covers emerging requirements and what are the most exciting/interesting memory technology developments that are on the horizon. 1) What are the driving requirements for the future in HPC and datacenters for the next decade, 2) How will both volatile and nonvolatile memory technologies evolve to meet those requirements? 3) How will the confluence of those two technologies change future system architectures (or how will these technologies increasingly differentiate to meet requirements?)

Dr. Jie Zhang will Join EECS of Peking University


Congratulation to Dr. Jie Zhang! He passed all the reviews of Peking University, and got the official letter to join the School of Electronics Engineering and Computer Science (EECS) of Peking University as an assistant professor from this summer. Peking University is one of the top public universities in China, which is ranked #23 in QS World University Rankings 2021. Dr. Zhang joined CAMEL at 2014, when we were located at the University of Texas at Dallas. He moved together with us to Korea and achieved a Ph.D. at 2020. After graduation, he spends around two years as a Postdoc at KAIST. While Dr. Zhang pursues Ph.D. at CAMEL, his researches are published in the most top venues such as ISCA, ASPLOS, MICRO, HPCA, OSDI, and FAST. He is well-deserved, and we believe that he will go beyond. This is great for both Dr. Zhang and Peking University! Congratulations Dr. Jang, and the best wish for your new journey!

CAMEL has been awarded with software computing fundamental technology research from Ministory of Science and ICT


Ministry of Science and ICT (IITP) awards CAMEL for AI-augmented Flash-based storage for self-driving car research. Specifically, CAMEL will perform the research of machine-learning algorithms that recover all runtime and device faults observed in automobiles. As the reliability of storage devices has a significant impact on self-driving automobiles, self-governing algorithms and fault-tolerant hardware architecture are significantly important. Prof. Jung as a single PI will be supported by around $1.6 million USD to develop lightweight machine-learning algorithms, hardware automation technology, and computer architecture for reliable storage and self-driving automobiles. We sincerely appreciate all anonymous reviewers and IITP staffs that gave us valuable comments and feedback!

Prof. Jung is awarded for ICT creative fusion research from Samsung Science & Technology Foundation


The Samsung Science & Technology Foundation awards Prof. Jung's team (Prof. Shinhyun Choi and Wanyeong Jung) with $1.2 million USD for emerging graph neural network (GNN) research. This is the first research of the Samsung Science & Technology Foundation, which punches through all components from OS to computer architecture/circuits to materials. This multidisciplinary approach builds new resistive random access memory (ReRAM) array that contains multiple bits per cell and the history of the inputs in a natural way and integrates all the memory materials to a silicon-fabricated device and processor. As the PI, Prof. Jung will investigate OS and AI system frameworks to make GNN more efficient and be deployed in many computing areas easily. Congratulations!

Read more: [ News at EE KAIST (Korean) ]

Jie's Memory over Storage solution has been accepted from ISCA 2021


Large persistent memories such as NVDIMM have been perceived as disruptive memory technology because they can maintain the state of a system even after a power failure and allow the system to recover quickly. However, overheads incurred by a heavy software-stack intervention seriously negate the benefits of such memories. First, to significantly reduce the software stack overheads, we propose HAMS, a hardware automated Memory-over-Storage (MoS) solution. Specifically, HAMS aggregates the capacity of NVDIMM and ultra-low latency flash archives (ULL-Flash) into a single large memory space, which can be used as a working or persistent memory expansion, in an OS-transparent manner. HAMS resides in the memory controller hub and manages its MoS address pool over conventional DDR and NVMe interfaces; it employs a simple hardware cache to serve all the memory requests from the host MMU after mapping the storage space of ULL-Flash to the memory space of NVDIMM. Second, to make HAMS more energy-efficient and reliable, we propose an "advanced HAMS" which removes unnecessary data transfers between NVDIMM and ULL-Flash after optimizing the datapath and hardware modules of HAMS. This approach unleashes the ULL-Flash and its NVMe controller from the storage box and directly connects the HAMS datapath to NVDIMM over the conventional DDR4 interface. Our evaluations show that HAMS and advanced HAMS can offer 97% and 119% higher system performance than a software-based hybrid NVDIMM design, while consuming 41% and 45% lower system energy, respectively. This year, the acceptance rate of ISCA is 18%. Congratulations!

Prof. Jung is awarded the best young researcher and granted with mid-scale research


The National Research Foundation of Korea awards Prof. Jung (and his lab, CAMEL) the best young researcher. The award is given by evaluating the performance of the principal investigator and checking future potential to create a new research area. CAMEL will be given by around $1 million USD and supported by the National Research Foundation for the next five years. We will perform diverse low-latency storage system solutions and cross-layer optimizations for enterprise/datacenter flash devices. The future plan, in particular, includes zero-overhead journaling computational storage, file system delegation, lock-free storage systems, hardware-accelerated operating system, and reliability management in enterprise servers. We sincerely appreciate all anonymous reviewers and NRF staffs that gave us valuable comments and feedback!

Wonil joins Hanyang University as a tenure-track professor


Dr. Wonil Choi joins Hanyang University this year as an assistant professor. He joined CAMEL when we were located at the University of Texas at Dallas (2013). After CAMEL moved to Korea (Yonsei University), he kept pursuing a Ph.D. at PennState (co-advised with Dr. Kandemir). He published 19 research papers with us at top-venues in computer architecture and operating systems areas. We remember him as an excellent student and active member in terms of not only research but also all other perspectives. At the end of his Ph.D. journey, he decides to join Hanyang University. His main research area is flash devices, storage, and firmware and file systems. All the best for his new position! Hope that this job will bring some fun and success to his life. Congratulation!

Read relaxation for 3D NAND work has been accepted from HPCA 2021


The adoption of 3D NAND has significantly increased the SSD density; however, 3D NAND density-increasing techniques, such as extensive stacking of cell layers, can amplify read disturbances and shorten SSD lifetime. From our lifetime-impact characterization on 8 state-of-the-art SSDs, we observe that the 3D TLC/QLC SSDs can be worn-out by low read-only workloads within their warranty period since a huge amount of read disturbance-induced rewrites are performed in the background. To understand alternative read disturbance mitigation opportunities, we also conducted read-latency characterizations on 2 other SSDs without the background rewrite mechanism. The collected results indicate that, without the background rewriting, the read latencies of the majority of data become higher, as the number of reads on the data increases. Motivated by these two characterizations, in this paper, we propose to relax the short read latency constraint on the high-density 3D SSDs. Specifically, our proposal relies on the hint information passed from applications to SSDs that specifies the expected read performance. By doing so, the lifetime consumption caused by the read-induced writes can be reduced, thereby prolonging the SSD lifetime. The detailed experimental evaluations show that our proposal can reduce up to 56\% of the rewrite-induced spent-lifetime with only 2\% lower performance, under a file-server application. The acceptance rate of ASPLOS this year is 18%

Our collaborative research related to 3D NAND has been accepted from HPCA 2021


The high-density of 3D NAND-based SSDs comes with longer write latencies due to the increasing program complexity. To address this write performance degradation issue, NAND flash manufacturers implement a 3D NAND-specific full-sequence program (FSP) operation. The FSP can program multiple-bit information into a cell simultaneously with the same latency as the baseline program operation, thereby dramatically boosting the write performance. However, directly adopting the (large granularity) FSP operation in SSD firmware can result in a lifetime degradation problem, where small writes are amplified to large granularities with a significant fraction of empty data. This problem cannot completely be mitigated by the DRAM buffer in the SSDs since the ``sync" commands from the host prevent the DRAM buffer from accumulating enough written data. To solve this FSP-induced performance/lifetime dilemma, in this work, we propose GSSA (Generalized and Specialized Scramble Allocation), a novel written-data allocation scheme in SSD firmware, which considers both various 3D NAND program operations and the internal 3D NAND flash architecture. By adopting GSSA, SSDs can enjoy the performance benefits brought by the FSP without excessively consuming the lifetime. Our experimental evaluations reveal that GSSA can achieve the throughput and the spent-lifetime of the best-performance and best-lifetime single granularity schemes, respectively. The acceptance rate of HPCA this year is 24%

We will have a Keynote speech for Samsung Open Source Conference 2020


Samsung Open Source Conference is currently the largest Open Source conference in Korea organized by Samsung Electronics. The conference has been held every year as a venue for more than 2,000 participants, such as software developers, students, and startup communities, to share their varied knowledge and experiences acquired from the Open Source field. We will have a Keynote speech that introduces diverse open-source hardware platforms, including processor IPs (RISC-V), memory controller IPs (SoftMC), AI accelerator IPs (NVDLA), and NVMe storage controller IPs (OpenExpress). It also shows what KAIST does for open source community, and what the industry/academia and products will take advantage of open-source hardware. Specifically, we will show an ecosystem of RISC-V and some other exciting projects that utilize open hardware such as automobile perception computing unit (Autoware.IO), open robotics (PULP), high-performance supercomputers (European Processor Initiative), and datacenters (XuanTie910 RISC-V).

CAMELab has got attention from diverse major press reports


OpenExpress has debuted to many major press reports such as Chosun (조선일보), Donga (동아일보), Hankyung (한국경제), and more than 50+ journals at the headlines of NAVER news and DAUM news. OpenExpress is a set of NVMe controller hardware IP modules and firmware for future fast storage class memory research with storage and memory communities. The cost of 3rd party's IP cores (maybe similar to OpenExpress ) is around $100K (USD) per single-use source code, but OpenExpress is free to download for academic research purposes. For the detailed new scraps (지면) and on-line articles, please check the follow:

[ KR news 45+ (Naver) ] [ KR major print press/newspaper 5+ ]

Gyuyoung's PRAM-based SSD work has been accepted from ICCAD'20


We propose Automatic-SSD that converts all storage management logic into hardware, which enable energy efficient, high performance fast memory based block storage. To achieve low operating power, Automatic-SSD directly reads or writes host-side data to underlying backend storage media without internal DRAM caches. To realize such DRAM-less approach with better performance and make it more energy efficient, Automatic-SSD also removes the internal processor(s) and firmware execution therein by fully automating the backend request management and data transfers over all pipelined hardware modules. We prototype Automatic-SSD on a middle-end FPGA custom board, employing massive numbers of phase change memories as representative of new memory technologies. Our evaluation results show that, compared to a conventional firmware-based approach, Automatic-SSD shows up 28.8× and 25.4× better bandwidth and latency behaviors, respectively, while consuming only 5% of the total energy, on overage.

Jie's work removing page victimiation overhead in NVMe, has been accepted from IEEE CAL'20


Host-side page victimizations can easily overflow the SSD internal buffer, which interferes I/O services of diverse user applications thereby degrading user-level experiences. To address this, we propose FastDrain, a co-design of OS kernel and flash firmware to avoid the buffer overflow, caused by page victimizations. Specifically, FastDrain can detect a triggering point where a near-future page victimization introduces an overflow of the SSD internal buffer. Our new flash firmware then speculatively scrubs the buffer space to accommodate the requests caused by the page victimization. In parallel, our new OS kernel design controls the traffic of page victimizations by considering the target device buffer status, which can further reduce the risk of buffer overflow. To secure more buffer spaces, we also design a latency-aware FTL, which dumps the dirty data only to the fast flash pages. Our evaluation results reveal that FastDrain reduces the 99th response time of user applications by 84%, compared to a conventional system.

Our acceleration NVMe I/O processing work has been accepted from USENIX ATC'20


NVMe is widely used by diverse types of SSDs and non-volatile memories as a de-facto fast I/O communication interface. Industry secures their own intellectual property (IP) for high-speed NVMe controllers and explores software stack challenges atop future fast NVMe devices. Unfortunately, such NVMe controller IPs are often inaccessible to academia. The research community however requires an open-source hardware framework to build new storage stack and controllers for the fast NVMe devices. We present OpenExpress, a fully hardware automated NVMe controller that has no software intervention to process concurrent I/O requests while supporting scalable data submission, rich outstanding NVMe command queues, and submission/completion queue management. The acceptance rate of ATC 2020 is around 18%.

Jie's GPU multi-processor with new flash has been accepted from ISCA'20


We propose ZnG, a new GPU-SSD integrated architecture, which can maximize the memory capacity in a GPU and address performance penalties imposed by an SSD. Specifically, ZnG replaces all GPU internal DRAMs with an ultra-lowlatency SSD to maximize the GPU memory capacity. ZnG further removes performance bottleneck of the SSD by replacing its flash channels with a high-throughput flash network and integrating SSD firmware in the GPU’s MMU to reap the benefits of hardware accelerations. Although flash arrays within the SSD can deliver high accumulated bandwidth, only a small fraction of such bandwidth can be utilized by GPU’s memory requests due to mismatches of their access granularity. To address this, ZnG employs a large L2 cache and flash registers to buffer the memory requests. Our evaluation results indicate that ZnG can achieve 7.5× higher performance than prior work. The acceptance rate of ISCA 2020 is 18%. Congratulations, Jie!

Miryeong, Donghyun, and Changrim's DC-Store work has been accepted from FAST'20


We propose DC-store, a storage framework that offers deterministic I/O performance for a multi-container execution environment. DC-store’s hardware-level design implements multiple NVM sets on a shared storage pool, each providing a deterministic SSD access time by removing internal resource conflicts. In parallel, software support of DC-Store is aware of the NVM sets and enlightens Linux kernel to isolate noisy neighbor containers, performing page frame reclaiming, from peers. We prototype both hardware and software counterparts of DC-Store and evaluate them in a real system. The evaluation results demonstrate that containerized data-intensive applications on DC-Store exhibit 31% shorter average execution time, on average, compared to those on a baseline systemThe acceptance rate of FAST 2020 is 16%. Congratulations, Miryeong!

Jie&Miryeong's scalable parallell flash firmware research has been accepted from FAST 2020


NVMe is designed to unshackle flash from a traditional storage bus, by allowing hosts to employ many threads to achieve higher bandwidth. While NVMe enables users to fully exploit all levels of parallelism offered by modern SSDs, current firmware designs are not scalable and have difficulty handling a large number of I/O requests in parallel due to its limited computation power and many hardware contentions. We propose DeepFlash, a novel manycore-based storage platform that can simultaneously process more than a million I/O requests in a second while hiding the long latency imposed by internal flash media. Inspired by a parallel data analysis system, we design the firmware based on many-to-many threading model that can be scaled horizontally. The proposed DeepFlash can extract the maximum performance of the underlying flash memory complex by concurrently executing multiple firmware components across many cores within the device. To show its extreme parallel scalability, we implement DeepFlash on a many-core prototype processor that employs dozens of lightweight cores, analyze new challenges from parallel I/O processing, and address the challenges by applying concurrency-aware optimizations. Our comprehensive evaluation reveals that DeepFlash can serve around 4.5 GB/s, while minimizing the CPU demand on microbenchmarks and real server workloads. The acceptance rate of FAST 2020 is 16%. Congratulations, Jie!

Wonil's consolidated flash cache has been accepted from ASPLOS 2020


Consolidating multiple workloads on a single flash-based storage device is now a common practice. We identify a new problem related to lifetime management in such settings: how should one partition device resources among consolidated workloads such that their allowed contributions to the device's wear (resulting from their writes including hidden writes due to garbage collection) may be deemed fairly assigned? This problem is made challenging by the complex relationship between hidden writes and allocated flash capacity. We first clarify why the write attribution problem is non-trivial. We then present a technique for it inspired by the Shapley value, a classical concept from cooperative game theory, and demonstrate that it is accurate, fair, and feasible. We next consider how to treat an overall "write budget" (i.e., total allowable writes during a given time period) for the device as a first-class resource worthy of explicit management. Towards this, we propose a novel write budget allocation technique (accompanied by a complementary capacity partitioning technique). Finally, we construct a dynamic lifetime management framework for consolidated devices by putting the above elements together. The acceptance rate of ASPLOS 2020 is 18%. Congratulations, Wonil!

Jie and Gyuyoung's work (co-first author) has been accepted from HPCA 2020


General purpose hardware accelerators have become major data processing resources in many computing domains. However, the processing capability of hardware accelerations is often limited by costly software interventions and memory copies to support compulsory data movement between different processors and solid-state drives (SSDs). This in turn also wastes a significant amount of energy in modern accelerated systems. In this work, we propose, DRAM-less, a hardware automation approach that precisely integrates many state-of-the-art phase change memory (PRAM) modules into its data processing network to dramatically reduce unnecessary data copies with a minimum of software modifications. We implement a new memory controller that plugs a real 3x nm multi-partition PRAM to 28nm technology FPGA logic cells and interoperate its design into a real PCIe accelerator emulation platform. The acceptance rate of HPCA-26 is 19%. Congratulations, Jie and Gyuyoung!

Sungjoon's Faster than Flash work has been accepted from IISWC'19


Emerging storage systems with new flash exhibit ultra-low latency (ULL) can address performance disparities between main memories and conventional solid state drives (SSDs) in memory hierarchy. Considering the low-latency characteristics, new types of I/O completion methods (polling) and storage stack architecture (SPDK) are proposed. While these new techniques are expected to take costly software interventions off the critical path in ULL SSDs, there is unfortunately no study to quantitatively analyze system-level characteristics and challenges by putting the techniques with real ULL devices. In this work, we first comprehensively perform empirical evaluations with 800GB ULL SSD prototypes and characterize ULL behaviors by considering a wide range of I/O path parameters such as different queues and access patterns. We then analyze the efficiencies and challenges of the polled-mode and hybrid polling I/O completion methods (added into Linux 4.4 and 4.10, respectively) and compare them with the efficiencies of a conventional interrupt-based I/O path. In addition, we revisit the common expectation of the SPDK by examining different types of system resources and performance parameters. We then demonstrate the challenges of ULL SSDs in a real SPDK-enabled server-client system. Based on the performance characteristics that this study uncovers, we also discuss several system implications, which are required to take a full advantage of ULL SSD in the future.

Wonil's dominant resource fairness has been accepted from USENIX HotStorage'19


We believe that, along with bandwidth and capacity, lifetime is also a critical resource and it needs to be explicitly and carefully managed in consolidated flash systems. To manage these diverse resources and fairly divide them across competing users in a consolidated flash device, we propose to employ dominant resource fairness (DRF). Using DRF, we empirically show that, managing only bandwidth and capacity shortens the device lifetime. In adapting DRF to the flash storage context, we identify a few challenges and present simple heuristics to overcome them. We also discuss possible design choices, which will be fully explored in future work.

Wonil's GC scheduling work has been accepted from IEEE TCAD


Garbage collection (GC) and resource contention on I/O buses (channels) are among the critical bottlenecks in solid-state disks (SSDs) that cannot be easily hidden. Most existing I/O scheduling algorithms in the host interface logic (HIL) of state-of-the-art SSDs are oblivious to such low-level performance bottlenecks in SSDs. As a result, SSDs may violate quality of service (QoS) requirements by not being able to meet the deadlines of I/O requests. In this paper, we propose a novel host interface I/O scheduler that is both GC aware and QoS aware. The proposed scheduler redistributes the GC overheads across non-critical I/O requests and reduces channel resource contention. Our experiments with workloads from various application domains revealed that the proposed client-level SSD scheduler reduces the standard deviation for latency by 52.5% and the worst-case latency by 86.6%, compared to the state- of-the-art I/O schedulers used for the HIL. In addition, for I/O requests smaller than a superpage, the proposed scheduler avoids channel resource conflicts and reduces latency by 29.2% in comparison to the state-of-the-art I/O schedulers. Furthermore, we present an extension of the proposed I/O scheduler for enterprise SSDs based on the NVMe protocol.

History before KAIST (2013.08~2019.02) HERE