Public bug reported:
Hi Ubuntu,
Just found out today that when using Ubuntu Xenial HWE kernel 4.13 in a
VM on top of Proxmox VE 5.1.x, the direct synchronous write performance
is 93% slower than on kernel 4.4. Kernel 4.13 direct sync 4KB write
could only achieve 303KB/s while kernel 4.4 could achieve 4.5MB/s.
The VM is using ext4 filesystem and running on top of ZFS ZVOL on ZFS
RAID1 with virtio-scsi, qemu disk cache none, and qemu disk discard
enabled. The underlying physical disks are Samsung Enterprise SSD SM863a
480GB series.
The reason I need to run kernel 4.13 to mount CephFS Luminous with
kernel client. Hopefully CephFS Luminous kernel client will be back
ported to kernel 4.4 in the near future.
Is this from Ubuntu Xenial kernel 4.13 performance regression or from
Proxmox VE 5.1 kernel 4.13 virtio-scsi performance regression?
The test results:
##
# ubuntu xenial kernel 4.13. the direct synchronous write performance is 93%
slower than kernel 4.4
##
root@localhost:~# uname -a
Linux localhost 4.13.0-37-generic #42~16.04.1-Ubuntu SMP Wed Mar 7 16:03:28 UTC
2018 x86_64 x86_64 x86_64 GNU/Linux
root@localhost:~# dd if=/dev/zero of=/mnt/test/test bs=4K count=256
oflag=direct,sync status=progress; rm /mnt/test/test
1048576 bytes (1.0 MB, 1.0 MiB) copied, 3.46369 s, 303 kB/s
##
# ubuntu xenial kernel 4.4. the direct synchronous write performance is 14x
faster than kernel 4.13
##
root@localhost:~# uname -a
Linux localhost 4.4.0-116-generic #140-Ubuntu SMP Mon Feb 12 21:23:04 UTC 2018
x86_64 x86_64 x86_64 GNU/Linux
root@localhost:~# dd if=/dev/zero of=/mnt/test/test bs=4K count=256
oflag=direct,sync status=progress; rm /mnt/test/test
1048576 bytes (1.0 MB, 1.0 MiB) copied, 0.231176 s, 4.5 MB/s
ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: linux-image-4.13.0-37-generic 4.13.0-37.42~16.04.1
ProcVersionSignature: Ubuntu 4.13.0-37.42~16.04.1-generic 4.13.13
Uname: Linux 4.13.0-37-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.15
Architecture: amd64
Date: Sun Mar 25 13:43:34 2018
InstallationDate: Installed on 2018-03-22 (2 days ago)
InstallationMedia: Ubuntu-Server 16.04.4 LTS "Xenial Xerus" - Release amd64
(20180228)
ProcEnviron:
TERM=screen-bce
PATH=(custom, no user)
XDG_RUNTIME_DIR=<set>
LANG=en_US.UTF-8
SHELL=/bin/bash
SourcePackage: linux-hwe
UpgradeStatus: No upgrade log present (probably fresh install)
** Affects: linux-hwe (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug xenial
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https://bugs.launchpad.net/bugs/1758621
Title:
Ubuntu Xenial HWE Kernel 4.13 Direct Sync Write Performance Regression
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