Bug 1322912

Summary:	The iscsi-initiator-utils iscsid uselessly changes the priority of the iscsi-wq rescue thread to -20
Product:	Red Hat Enterprise Linux 6	Reporter:	Richard Sharpe <realrichardsharpe>
Component:	iscsi-initiator-utils	Assignee:	Chris Leech <cleech>
Status:	CLOSED WONTFIX	QA Contact:	Martin Hoyer <mhoyer>
Severity:	unspecified	Docs Contact:
Priority:	unspecified
Version:	6.7	CC:	agrover, coughlan, mhoyer
Target Milestone:	rc
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:	2017-12-06 10:26:09 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:

Description Richard Sharpe 2016-03-31 15:58:48 UTC

When you use iscsiadm (or automatic login) iscsid does the login, and then after creating the session in the kernel, it iterates through /proc/<pid>/stat looking for a thread named iscsi-q-NN where NN is the iSCSI session number.

When it finds that thread, it sets the priority (nice) to -20.

There are two problems:

1. That is the rescue thread and the vast majority of iSCSI work items are not processed on that thread.

2. It is created at nice -20.

This is an enormous waste of time and is a big impact when you are trying to start up hundreds if iSCSI sessions after a node failover.

This most likely applies to RHEL 7.x as well. It applies to kernels from at least 3.10.0 and above. I have not checked earlier kernels but the problem probably started with the new WorkQueue approaches (pools etc.)

It is very reproducible.

I posted a patch on the open-iscsi mailing list about this as well:

https://groups.google.com/forum/#!topic/open-iscsi/tC9arPRJ1RY

I can attach the patch if needed.

Comment 1 Chris Leech 2016-03-31 16:03:33 UTC

(In reply to Richard Sharpe from comment #0)
> I posted a patch on the open-iscsi mailing list about this as well:
> 
> https://groups.google.com/forum/#!topic/open-iscsi/tC9arPRJ1RY
> 
> I can attach the patch if needed.

Thank you for the detailed report, and for taking this to the open-iscsi mailing list as well.

No need to attach patches here for now, lets deal with this on the upstream open-iscsi list and I'll take it from there into RHEL.

Comment 3 Jan Kurik 2017-12-06 10:26:09 UTC

Red Hat Enterprise Linux 6 is in the Production 3 Phase. During the Production 3 Phase, Critical impact Security Advisories (RHSAs) and selected Urgent Priority Bug Fix Advisories (RHBAs) may be released as they become available.

The official life cycle policy can be reviewed here:

http://redhat.com/rhel/lifecycle

This issue does not meet the inclusion criteria for the Production 3 Phase and will be marked as CLOSED/WONTFIX. If this remains a critical requirement, please contact Red Hat Customer Support to request a re-evaluation of the issue, citing a clear business justification. Note that a strong business justification will be required for re-evaluation. Red Hat Customer Support can be contacted via the Red Hat Customer Portal at the following URL:

https://access.redhat.com/