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Bug 1930320 - virtio-blk with iothreads can be significantly slower than without
Summary: virtio-blk with iothreads can be significantly slower than without
Keywords:
Status: CLOSED CURRENTRELEASE
Alias: None
Product: Red Hat Enterprise Linux 9
Classification: Red Hat
Component: qemu-kvm
Version: unspecified
Hardware: Unspecified
OS: Unspecified
high
high
Target Milestone: rc
: ---
Assignee: Stefan Hajnoczi
QA Contact: Tingting Mao
URL:
Whiteboard:
Depends On:
Blocks: 1827722
TreeView+ depends on / blocked
 
Reported: 2021-02-18 16:50 UTC by Stefan Hajnoczi
Modified: 2022-08-09 15:01 UTC (History)
12 users (show)

Fixed In Version:
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
Environment:
Last Closed: 2022-08-09 15:01:38 UTC
Type: Bug
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)

Description Stefan Hajnoczi 2021-02-18 16:50:39 UTC 
Description of problem:
In some cases virtio-blk with iothreads is ~30% slower than without. These cases need to be investigated because enabling iothreads is supposed to improve performance across the board.

One example is randwrite,bs=64kb,iodepth=1 with 16 threads.

http://kvm-perf.englab.nay.redhat.com/results/regression/multiqueue_rhel8.4.0/dataplane/4queues/raw.virtio_blk.*.x86_64.html

Version-Release number of selected component (if applicable):
qemu-kvm-5.2.0-1.module+el8.4.0+9091+650b220a

How reproducible:


Steps to Reproduce:
See benchmark details above.

Actual results:
~30% slower with iothreads in some cases.

Expected results:
iothreads should be similar or faster than without iothreads.


Additional info:
Comment 1 John Ferlan 2021-09-09 11:27:16 UTC 
Bulk update: Move RHEL-AV bugs to RHEL9. If necessary to resolve in RHEL8, then clone to the current RHEL8 release.
Comment 2 Klaus Heinrich Kiwi 2022-01-19 16:55:00 UTC 
Stefan,
 
Do you think this one is doable for RHEL9 investigation / inclusion?
Comment 3 Stefan Hajnoczi 2022-01-24 17:24:30 UTC 
(In reply to Klaus Heinrich Kiwi from comment #2)
> Do you think this one is doable for RHEL9 investigation / inclusion?

I have too many ongoing tasks at the moment. It's possible that some of the optimizations I've been working on will apply to this BZ but I can't commit to it for RHEL9.
Comment 5 Tingting Mao 2022-07-27 07:09:02 UTC 
Hi Stefan,

After tried in latest rhel9.1, there is just a little performance degradation(~3%) for several combinations of read, but most of them, the performance is better after adding the iothread.

Check below link for the details:
http://kvm-perf.englab.nay.redhat.com/results/regression/nvme9.1.0_qemu7.0.0-9_kernel5.14.0-96_iothread/raw.virtio_blk.*.x86_64.html 

Could you please check again? I think we could close this bug as currentrelease then.

Thanks.
Comment 6 Stefan Hajnoczi 2022-08-09 15:01:38 UTC 
(In reply to Tingting Mao from comment #5)
> Hi Stefan,
> 
> After tried in latest rhel9.1, there is just a little performance
> degradation(~3%) for several combinations of read, but most of them, the
> performance is better after adding the iothread.
> 
> Check below link for the details:
> http://kvm-perf.englab.nay.redhat.com/results/regression/nvme9.1.0_qemu7.0.0-
> 9_kernel5.14.0-96_iothread/raw.virtio_blk.*.x86_64.html 
> 
> Could you please check again? I think we could close this bug as
> currentrelease then.
> 
> Thanks.

Thanks, I agree performance looks acceptable and we can close this bug.
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