Comment 0 for bug 1847948

== Comment: #0 - Murilo Opsfelder Araujo - 2019-10-11 14:16:14 ==

---Problem Description---
Back-port the following patches to Bionic QEMU to improve NVMe guest performance by more than 200%:

?vfio-pci: Allow mmap of MSIX BAR?
https://git.qemu.org/?p=qemu.git;a=commit;h=ae0215b2bb56a9d5321a185dde133bfdd306a4c0

?ppc/spapr, vfio: Turn off MSIX emulation for VFIO devices?
https://git.qemu.org/?p=qemu.git;a=commit;h=fcad0d2121976df4b422b4007a5eb7fcaac01134

---uname output---
na

---Additional Hardware Info---
0030:01:00.0 Non-Volatile memory controller: Samsung Electronics Co Ltd NVMe SSD Controller 172Xa/172Xb (rev 01)

Machine Type = AC922

---Debugger---
A debugger is not configured

---Steps to Reproduce---
 Install or setup a guest image and boot it.

Once guest is running, passthrough the NVMe disk to the guest using the XML:

host$ cat nvme-disk.xml
<hostdev mode='subsystem' type='pci' managed='no'>
   <driver name='vfio'/>
    <source>
        <address domain='0x0030' bus='0x01' slot='0x00' function='0x0'/>
    </source>
</hostdev>

host$ virsh attach-device <domain> nvme-disk.xml --live

On the guest, run fio benchmarks:

guest$ fio --direct=1 --rw=randrw --refill_buffers --norandommap --randrepeat=0 --ioengine=libaio --bs=4k --rwmixread=100 --iodepth=16 --runtime=60 --name=job1 --filename=/dev/nvme0n1 --numjobs=4

Results are similar with numjobs=4 and numjobs=64, respectively:

   READ: bw=385MiB/s (404MB/s), 78.0MiB/s-115MiB/s (81.8MB/s-120MB/s), io=11.3GiB (12.1GB), run=30001-30001msec
   READ: bw=382MiB/s (400MB/s), 2684KiB/s-12.6MiB/s (2749kB/s-13.2MB/s), io=11.2GiB (12.0GB), run=30001-30009msec

With the two patches applied, performance improved significantly for numjobs=4 and numjobs=64 cases, respectively:

   READ: bw=1191MiB/s (1249MB/s), 285MiB/s-309MiB/s (299MB/s-324MB/s), io=34.9GiB (37.5GB), run=30001-30001msec
   READ: bw=4273MiB/s (4481MB/s), 49.7MiB/s-113MiB/s (52.1MB/s-119MB/s), io=125GiB (134GB), run=30001-30005msec

Userspace tool common name: qemu

Userspace rpm: qemu

The userspace tool has the following bit modes: 64-bit

Userspace tool obtained from project website: na