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Bug 2104407

Summary: RFE: support to get thread-pool-max/thread-pool-min by domstats
Product: Red Hat Enterprise Linux 9 Reporter: Han Han <hhan>
Component: libvirtAssignee: Virtualization Maintenance <virt-maint>
libvirt sub component: General QA Contact: Virtualization Bugs <virt-bugs>
Status: CLOSED WONTFIX Docs Contact:
Severity: unspecified    
Priority: unspecified CC: coli, mprivozn, pkrempa, qinwang, virt-maint
Version: 9.1Keywords: FutureFeature
Target Milestone: rcFlags: 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: 2022-07-12 07:53:34 UTC Type: Feature Request
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: 2104404    
Bug Blocks:    

Description Han Han 2022-07-06 07:50:00 UTC 
Description of problem:
As subject

Version-Release number of selected component (if applicable):
libvirt-8.5.0-1.el9.x86_64
qemu-kvm-7.0.0-8.el9.x86_64

How reproducible:
100%

Steps to Reproduce:
1. Start a VM with thread-pool-max/thread-pool-min properties:
➜  ~ virsh domstate rhel
running

➜  ~ virsh dumpxml rhel --xpath //iothread       
<iothread id="2" thread_pool_min="2" thread_pool_max="10"/>
<iothread id="4"/>
<iothread id="6"/>
<iothread id="8" thread_pool_min="2" thread_pool_max="32"/>
<iothread id="1"/>
<iothread id="5"/>
<iothread id="7"/>

Try querying thread-pool-max/thread-pool-min by `virsh domstats --iothread`
➜  ~ virsh domstats rhel --iothread                                        
Domain: 'rhel'
  iothread.count=7
  iothread.2.poll-max-ns=32768
  iothread.2.poll-grow=0
  iothread.2.poll-shrink=0
  iothread.8.poll-max-ns=32768
  iothread.8.poll-grow=0
  iothread.8.poll-shrink=0
  iothread.1.poll-max-ns=32768
  iothread.1.poll-grow=0
  iothread.1.poll-shrink=0
  iothread.7.poll-max-ns=32768
  iothread.7.poll-grow=0
  iothread.7.poll-shrink=0
  iothread.6.poll-max-ns=32768
  iothread.6.poll-grow=0
  iothread.6.poll-shrink=0
  iothread.5.poll-max-ns=32768
  iothread.5.poll-grow=0
  iothread.5.poll-shrink=0
  iothread.4.poll-max-ns=32768
  iothread.4.poll-grow=0
  iothread.4.poll-shrink=0

No thread-pool-max/thread-pool-min properties.

Actual results:
As above

Expected results:
As subject

Additional info:
QEMU doesn't support querying thread-pool-max/thread-pool-min as well.
The depended bug https://bugzilla.redhat.com/show_bug.cgi?id=2104404
Comment 2 Peter Krempa 2022-07-07 07:53:13 UTC 
The thread pool limits is in fact configuration of a VM and not really a statistic. I don't think this is a worthwhile addition to domain statistics which is mainly focused on data that depends on the running parameters of the VM
Comment 3 Michal Privoznik 2022-07-11 01:50:26 UTC 
Yeah, I don't see much value in reporting min/max values. If anything, then maybe the current size of the pool? And even then the interpretation of the number is doubtful. I mean, imagine min=1 max=10 and you'll find out that the current value is 10. Does it mean the iothread's pool is under pressure and has a lot of requests to process? No. At some point it decided to spawn 10 threads (maybe there was a spike in requests), but now there's no request to process at all. Or complete opposite and the iothread might indeed be the bottleneck.

Han, could you please expand on why you think these values should be reported?
Comment 4 Han Han 2022-07-12 03:14:57 UTC 
(In reply to Michal Privoznik from comment #3)
> Yeah, I don't see much value in reporting min/max values. If anything, then
> maybe the current size of the pool? And even then the interpretation of the
> number is doubtful. I mean, imagine min=1 max=10 and you'll find out that
> the current value is 10. Does it mean the iothread's pool is under pressure
> and has a lot of requests to process? No. At some point it decided to spawn
> 10 threads (maybe there was a spike in requests), but now there's no request
> to process at all. Or complete opposite and the iothread might indeed be the
> bottleneck.
> 
> Han, could you please expand on why you think these values should be
> reported?

This idea comes when I find the properties thread-pool-max/thread-pool-min cannot be queried by domstats. 
Now I agree that reporting the current size of the pool is more useful.
Comment 5 Michal Privoznik 2022-07-12 07:01:42 UTC 
But that's the thing I tired to explain in comment 3. What information can an user deduct from the current size of the pool?
Comment 6 Peter Krempa 2022-07-12 07:53:34 UTC 
As noted in Comment #2, domain configuration shouldn't really be mirrored in statistics and per Comment #3, reporting of current size of the pool is not a useful statistic.
Comment 7 Han Han 2022-08-01 02:41:06 UTC 
(In reply to Michal Privoznik from comment #5)
> But that's the thing I tired to explain in comment 3. What information can
> an user deduct from the current size of the pool?

Sorry for the late update. I am not clear.