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Bug 1930320

Summary:	virtio-blk with iothreads can be significantly slower than without
Product:	Red Hat Enterprise Linux 9	Reporter:	Stefan Hajnoczi <stefanha>
Component:	qemu-kvm	Assignee:	Stefan Hajnoczi <stefanha>
qemu-kvm sub component:	virtio-blk,scsi	QA Contact:	Tingting Mao <timao>
Status:	CLOSED CURRENTRELEASE	Docs Contact:
Severity:	high
Priority:	high	CC:	anton.wd, chayang, coli, jen, jinzhao, juzhang, kkiwi, ldoktor, qinwang, virt-maint, xuwei, yama
Version:	unspecified	Keywords:	Triaged
Target Milestone:	rc	Flags:	pm-rhel: mirror+
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:		Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2022-08-09 15:01:38 UTC	Type:	Bug
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:
Bug Blocks:	1827722

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.