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+-------------------------------------------------------------------------------+
| ConfZNS : A Novel Emulator for Exploring Design Space of ZNS SSDs             |
+-------------------------------------------------------------------------------+

[SYSTOR23 paper]

USAGE

How to Configure?

The current version of ConfZNS supports built-in configuration, so user have to compile confZNS for each setting(this will be change soon)

//Example in zns.c:1787
    spp->pg_rd_lat = NAND_READ_LATENCY;
    spp->pg_wr_lat = NAND_PROG_LATENCY;
    spp->blk_er_lat = NAND_ERASE_LATENCY;
    spp->ch_xfer_lat = NAND_CHNL_PAGE_TRANSFER_LATENCY;

    spp->nchnls         = 8;   //default : 8
    spp->chnls_per_zone = 1;   
    spp->zones          = n->num_zones;     
    spp->ways           = 2;    //default : 2
    spp->ways_per_zone  = 2;    //default :==spp->ways
    spp->dies_per_chip  = 1;    //default : 1
    spp->planes_per_die = 4;    //default : 4
    spp->register_model = 1;
  • to change configurations,
    • SU-zone
        spp->chnls_per_zone = 1;   
    spp->ways_per_zone  = 1;    //default :==spp->ways
    • MU4-zone
        spp->chnls_per_zone = 4;    
    spp->ways_per_zone  = 1;    //default :==spp->ways
    • MU8-zone
        spp->chnls_per_zone = 8;    
    spp->ways_per_zone  = 1;    //default :==spp->ways
    • FU-zone(16)
        spp->chnls_per_zone = 8;    
    spp->ways_per_zone  = 2;    //default :==spp->ways

How to support conventional zone?

  • In ConfZNS,
//in nvme.h : 40, 
#define MK_ZONE_CONVENTIONAL 5    // making 32(=2^5) conventional zones
  • In Guest Kernel (v5.10.2)
//in linux-5.10.2/driver/nvme/host/zns.c:146 

static int nvme_zone_parse_entry(struct nvme_ns *ns,
				 struct nvme_zone_descriptor *entry,
				 unsigned int idx, report_zones_cb cb,
				 void *data)
{
	struct blk_zone zone = { };

	if ((((entry->zt & 0xf) != NVME_ZONE_TYPE_SEQWRITE_REQ)&&((entry->zt & 0xf) != NVME_ZONE_TYPE_CONVENTIONAL))){
		return -EINVAL;
	}

	//zone.type = BLK_ZONE_TYPE_SEQWRITE_REQ;
	if((entry->zt & 0xf) == NVME_ZONE_TYPE_CONVENTIONAL){
		zone.type = BLK_ZONE_TYPE_CONVENTIONAL;
		dev_err(ns->ctrl->device, "[inho] conv to zidx %x\n",idx);
	}
	else {
		zone.type = BLK_ZONE_TYPE_SEQWRITE_REQ;
	}
	zone.cond = entry->zs >> 4;
	zone.len = ns->zsze;
	zone.capacity = nvme_lba_to_sect(ns, le64_to_cpu(entry->zcap));
	zone.start = nvme_lba_to_sect(ns, le64_to_cpu(entry->zslba));
	zone.wp = nvme_lba_to_sect(ns, le64_to_cpu(entry->wp));

	return cb(&zone, idx, data);
}
//in linux-5.10.2/include/linux/nvme.h:570

enum {
	NVME_ZONE_TYPE_CONVENTIONAL =0x1, 	
	NVME_ZONE_TYPE_SEQWRITE_REQ =0x2,
};

How to enable mixed zone?(Different paralelism support in ConfZNS)

You can set the 'is_another_namespace' parameter for different mapping to a zone

Here is an example to set [14 channels zone] + [2 channels zone] setting. In here, let us call these two zone groups as "namespace" 14 channels zone = ns0 2 channels zone = ns1

Configuration goes like

//Example in zns.c:1787
    spp->nchnls         = 16;   //default : 8
    spp->chnls_per_zone = 2;   
    spp->zones          = n->num_zones;     
    spp->ways           = 1;    //default : 2
    spp->ways_per_zone  = 1;    //default :==spp->ways
    spp->dies_per_chip  = 1;    //default : 1
    spp->planes_per_die = 4;    //default : 4
    spp->register_model = 1;

and

    spp->is_another_namespace = true;	//default : false
    spp->chnls_per_another_zone = 14;

spp->chnls_per_another_zone = 14; means allocate 14 channels to zone, where spp->nchnls = 16. Rest of the channels(in here, 2channels) will assigned to ns1, which is another zone groups.

This changes the zone mapping.

Here, example of 16 zones are configured as 14 channels zone. Starting from 17-th zone, all zones are configured as 2channels zone.

|LBA : 0 - zonesize * 16|  zonesize * 16 - dev size |
|<----- 16 zones ------>|<-------- N zones -------->|
| 14ch z | 14ch z | ..  | 2ch z | 2ch z |.. | 2ch z |

Host can access each zone by different lba, aligned with the zone size

If you want to change the border of each zone groups, change "(zidx < 16)" to some setting( e.g, < 32, < 1024, etc)

//Example in zns.c:123

static inline uint64_t zns_get_multiway_chip_idx(NvmeNamespace *ns, uint64_t slba){
    FemuCtrl *n = ns->ctrl;
    struct zns * zns = n->zns;
    struct zns_ssdparams *spp = &zns->sp;
    uint64_t zidx= zns_zone_idx(ns, slba);

    if (spp->is_another_namespace)
        return (zidx < 16) ? (zns_get_ns0_zone_ppn_idx(ns,slba)% (spp->nchnls * spp->ways)) : (zns_another_ns1_zone_ppn_idx(ns,slba) % (spp->nchnls * spp->ways)); 
    else{
        uint64_t ppn = zns_get_multichnlway_ppn_idx(ns,slba);
        return ((ppn/spp->planes_per_die) % (spp->nchnls * spp->ways));
    }
}
Installation (FEMU readme)

FEMU Version Build Status License: GPL v2 Platform

  ______ ______ __  __ _    _ 
 |  ____|  ____|  \/  | |  | |
 | |__  | |__  | \  / | |  | |
 |  __| |  __| | |\/| | |  | |
 | |    | |____| |  | | |__| |
 |_|    |______|_|  |_|\____/  -- A QEMU-based and DRAM-backed NVMe SSD Emulator

Contact Information

Maintainer: Huaicheng Li, Email: hcli AT cmu dot edu

Feel free to contact Huaicheng for any suggestions/feedback, bug reports, or general discussions.

Please consider citing our FEMU paper at FAST 2018 if you use FEMU. The bib entry is

@InProceedings{Li+18-FEMU, 
Author = {Huaicheng Li and Mingzhe Hao and Michael Hao Tong 
and Swaminathan Sundararaman and Matias Bj{\o}rling and Haryadi S. Gunawi},
Title = "The CASE of FEMU: Cheap, Accurate, Scalable and Extensible Flash Emulator",
Booktitle =  {Proceedings of 16th USENIX Conference on File and Storage Technologies (FAST)},
Address = {Oakland, CA},
Month =  {February},
Year =  {2018}
}

Research Papers using FEMU

Please Check the growing list of research papers using FEMU here, including papers at ASPLOS, OSDI, SOSP and FAST, etc.

Project Description (What is FEMU?)

                        +--------------------+
                        |    VM / Guest OS   |
                        |                    |
                        |                    |
                        |  NVMe Block Device |
                        +--------^^----------+
                                 ||
                              PCIe/NVMe
                                 ||
  +------------------------------vv----------------------------+
  |  +---------+ +---------+ +---------+ +---------+ +------+  |
  |  | Blackbox| |  OCSSD  | | ZNS-SSD | |  NoSSD  | | ...  |  |
  |  +---------+ +---------+ +---------+ +---------+ +------+  |
  |                    FEMU NVMe SSD Controller                |
  +------------------------------------------------------------+

Briefly speaking, FEMU is a fast, accurate, scalable, and extensible NVMe SSD Emulator. Based upon QEMU/KVM, FEMU is exposed to Guest OS (Linux) as an NVMe block device (e.g. /dev/nvme0nX). It supports emulating different types of SSDs:

  • Whitebox mode (OCSSD) (a.k.a. Software-Defined Flash (SDF), or OpenChannel-SSD) with host side FTL (e.g. LightNVM or SPDK FTL), both OpenChannel Spec 1.2 and 2.0 are supported.

  • Blackbox mode (BBSSD) with FTL managed by the device (like most of current commercial SSDs). A page-level mapping based FTL is included.

  • ZNS mode (ZNSSD), exposing NVMe Zone interface for the host to directly read/write/append to the device following certain rules.

  • NoSSD mode, emulating a as-fast-as-possible NVMe device with sub-10 microsecond latency. This is to emualte SCM-class block devices such as Optane or Z-NAND SSDs.

FEMU design aims to achieve the benefits of both SSD Hardware platforms (e.g. CNEX OpenChannel SSD, OpenSSD, etc.) and SSD simulators (e.g. DiskSim+SSD, FlashSim, SSDSim, etc.). Like hardware platforms, FEMU can support running full system stack (Applications + OS + NVMe interface) on top, thus enabling Software-Defined Flash (SDF) alike research with modifications at application, OS, interface or SSD controller architecture level. Like SSD simulators, FEMU can also support internal-SSD/FTL related research. Users can feel free to experiment with new FTL algorithms or SSD performance models to explore new SSD architecture innovations as well as benchmark the new arch changes with real applications, instead of using decade-old disk trace files.

Installation

  1. Make sure you have installed necessary libraries for building QEMU. The dependencies can be installed by following instructions below:
  git clone https://github.com/ucare-uchicago/femu.git
  cd femu
  mkdir build-femu
  # Switch to the FEMU building directory
  cd build-femu
  # Copy femu script
  cp ../femu-scripts/femu-copy-scripts.sh .
  ./femu-copy-scripts.sh .
  # only Debian/Ubuntu based distributions supported
  sudo ./pkgdep.sh
  1. Compile & Install FEMU:
  ./femu-compile.sh

FEMU binary will appear as x86_64-softmmu/qemu-system-x86_64

Tested host environment (For successful FEMU compilation):

Linux Distribution Kernel Gcc Ninja Python
Gentoo 5.10 9.3.0 1.10.1 3.7.9
Ubuntu 16.04.5 4.15.0 5.4.0 1.8.2 3.6.0
Ubuntu 20.04.1 5.4.0 9.3.0 1.10.0 3.8.2

Tested VM environment (Whether a certain FEMU mode works under a certain guest kernel version):

Mode \ Guest Kernel 4.16 4.20 5.4 5.10
NoSSD ✓ ✓ ✓ ✓
Black-box SSD ✓ ✓ ✓ ✓
OpenChannel-SSD v1.2 ✓ ✓ ✓ ✓
OpenChannel-SSD v2.0 ✗ ✓ ✓ ✓
Zoned-Namespace (ZNS) SSD ✗ ✗ ✗ ✓
  1. Prepare the VM image (For performance reasons, we suggest to use a server version guest OS [e.g. Ubuntu Server 20.04, 18.04, 16.04])

You can either build your own VM image, or use the VM image provided by us

Option 1: This is the recommended way to get FEMU running quickly - Use our VM image file. You can download it from our FEMU-VM-image-site. After you fill in the form, VM image downloading instructions will be sent to your email address shortly.

Option 2: Build your own VM image by following instructions: After the guest OS is installed, make following changes to redirect VM output to the console, instead of using a separate GUI window. (Desktop version guest OS is not tested)

Note: Please ask for help from Google if any of the steps doesn't work. In general, it gives you a basic idea to build your own VM image and make it run in text console.

    # Download a Ubuntu server ISO file
    $ mkdir -p ~/images/
    $ cd ~/images
    $ wget http://releases.ubuntu.com/20.04/ubuntu-20.04.3-live-server-amd64.iso
    $ sudo apt-get install qemu-system-x86
    # Create a QCOW2 disk image
    $ qemu-img create -f qcow2 femu.qcow2 80G

    # install guest OS to femu.qcow2 (You need a GUI environment to prepare the VM image)
    $ qemu-system-x86_64 -cdrom ubuntu-20.04.3-live-server-amd64.iso -hda femu.qcow2 -boot d -net nic -net user -m 8192 -localtime -smp 8 -cpu host -enable-kvm
  • After guest OS is installed, boot it with
    $ qemu-system-x86_64 -hda femu.qcow2 -net nic -net user -m 8192 -localtime -smp 8 -cpu host -enable-kvm

If the OS is installed into femu.qcow2, you should be able to enter the guest OS. Inside the VM, edit /etc/default/grub, make sure the following options are set.

GRUB_CMDLINE_LINUX="ip=dhcp console=ttyS0,115200 console=tty console=ttyS0"
GRUB_TERMINAL=serial
GRUB_SERIAL_COMMAND="serial --unit=0 --speed=115200 --word=8 --parity=no --stop=1"

Still in the VM, update the grub

$ sudo update-grub
$ sudo shutdown -h now

Now you're ready to Run FEMU. If you stick to a Desktop version guest OS, please remove "-nographics" command option from the running script before running FEMU.

  1. Login to FEMU VM
  • If you correctly setup the aforementioned configurations, you should be able to see text-based VM login in the same terminal where you issue the running scripts.
  • Or, more conveniently, FEMU running script has mapped host port 8080 to guest VM port 22, thus, after you install and run openssh-server inside the VM, you can also ssh into the VM via below command line. (Please run it from your host machine)
$ ssh -p8080 $user@localhost

Run FEMU

0. Minimum Requirement

  • Run FEMU on a physical machine, not inside a VM (if the VM has nested virtualization enabled, you can also give it a try, but FEMU performance will suffer, this is not recommended.)

  • At least 8 cores and 12GB DRAM in the physical machine to enable seamless run of the following default FEMU scripts emulating a 4GB SSD in a VM with 4 vCPUs and 4GB DRAM.

  • If you intend to emulate a larger VM (more vCPUs and DRAM) and an SSD with larger capacity, make sure refer to the resource provisioning tips here.

1. Run FEMU as blackbox SSDs (Device-managed FTL or BBSSD mode)

TODO: currently blackbox SSD parameters are hard-coded in hw/block/femu/ftl/ftl.c, please change them accordingly and re-compile FEMU.

Boot the VM using the following script:

./run-blackbox.sh

2. Run FEMU as whitebox SSDs (ak.a. OpenChannel-SSD or OCSSD mode)

Both OCSSD Specification 1.2 and Specification 2.0 are supported, to run FEMU OCSSD mode:

./run-whitebox.sh

By default, FEMU will run OCSSD in 2.0 mode. To run OCSSD in 1.2, make sure OCVER=1 is set in the run-whitebox.sh

Inside the VM, you can play with LightNVM.

3. Run FEMU without SSD logic emulation (NoSSD mode)

./run-nossd.sh

In this nossd mode, no SSD emulation logic (either blackbox or whitebox emulation) will be executed. Base NVMe specification is supported, and FEMU in this case handles IOs as fast as possible. It can be used for basic performance benchmarking, as well as fast storage-class memory (SCM, or Intel Optane SSD) emulation.

4. Run FEMU as NVMe ZNS (Zoned-Namespace) SSDs (ZNSSD mode)

Notes: Currently only basic ZNS interface is supported and it can be used for development purposes. More features like proper latency emulation, controller-level zone mappings to flash chips are work-in-progress.

./run-zns.sh

Contributing

Github issue and pull request are preferred. Do let us know if you have any thoughts!

Acknowledgement

FEMU is inspired by many prior SSD simulators/emulators (SSDSim, FlashSim, VSSIM) as well as hardware development platforms (OpenSSD, DFC), but FEMU has gone far beyond what prior platforms can achieve in terms of performance, extensibility, and usability.

FEMU's NVMe controller logic is based on QEMU/NVMe, LightNVM/QEMU and ZNS/QEMU.

For more detail, please checkout the Wiki!