Bug 1886738

Summary:	High number of context switches caused by VDO kernel threads while vdo volume is unused or idle
Product:	Red Hat Enterprise Linux 8	Reporter:	Nikolay Kichukov <nikolay>
Component:	kmod-kvdo	Assignee:	Ken Raeburn <raeburn>
Status:	CLOSED ERRATA	QA Contact:	Filip Suba <fsuba>
Severity:	medium	Docs Contact:
Priority:	unspecified
Version:	8.4	CC:	awalsh, corwin, cwei, emcnabb, fsuba, nikolay, raeburn
Target Milestone:	rc	Keywords:	Triaged
Target Release:	8.0
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:	6.2.5.71	Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2021-11-09 19:28:28 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:

Description Nikolay Kichukov 2020-10-09 09:37:42 UTC

Hi team,

This report is somehow related to and can be considered a continuation of: 
https://bugzilla.redhat.com/show_bug.cgi?id=1870660

We would be looking to minimize the number of context switches from the VDO threads this time.

Current state: starting VDO volumes that are not in use on an idle system increases the number of context switches with around 8000 context switches / second.

On an idle physical system with 4 CPUs running kernel 5.8.14 and kvdo-corp 6.2.4.14:

VDO devices are not started: 90 context switches / second
VDO devices(2 devices) are started and not used: 8000 context switches / second

The threads that consume the CPU seem to be:


 [kvdo2:packerQ]
 [kvdo2:ackQ]
 [kvdo2:cpuQ0]
 [kvdo2:cpuQ1]
 [kvdo3:dedupeQ]
 [kvdo3:journalQ]
 [kvdo3:hashQ0]
 [kvdo3:bioQ0]
 [kvdo3:bioQ1]
 [kvdo3:bioQ2]
 [kvdo3:bioQ3]
 [kvdo3:cpuQ0]
 [kvdo3:cpuQ1]

In an ideal world, having started an idling VDO volume should not increase the number of context switches on the system.

Thank you,
-Nikolay

Comment 1 Nikolay Kichukov 2021-02-22 19:48:41 UTC

Hi folks,
any progress update with this?

Comment 2 Ken Raeburn 2021-03-09 19:41:46 UTC

(In reply to Nikolay Kichukov from comment #1)
> Hi folks,
> any progress update with this?

Sorry, Nikolay, not so far. I've had another work item ahead of it in my queue... I'll be looking into it this week though.

Comment 6 Filip Suba 2021-08-16 13:08:10 UTC

Verified with kmod-kvdo-6.2.5.72-79.el8

Comment 9 errata-xmlrpc 2021-11-09 19:28:28 UTC

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (kmod-kvdo bug fix and enhancement update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2021:4359