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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.
(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.
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