Bug 430310 - [RHEL5.2]: In a domU, all tasks are taskset to cpu 0 by default
Summary: [RHEL5.2]: In a domU, all tasks are taskset to cpu 0 by default
Alias: None
Product: Red Hat Enterprise Linux 5
Classification: Red Hat
Component: kernel-xen
Version: 5.2
Hardware: All
OS: Linux
Target Milestone: rc
: ---
Assignee: Chris Lalancette
QA Contact: Martin Jenner
Keywords: Regression
Depends On:
TreeView+ depends on / blocked
Reported: 2008-01-25 23:58 UTC by Chris Lalancette
Modified: 2008-05-21 15:08 UTC (History)
6 users (show)

Clone Of:
Last Closed: 2008-05-21 15:08:03 UTC

Attachments (Terms of Use)
Patch to fix the problem where init is only set to vcpu 0 (456 bytes, patch)
2008-01-26 00:48 UTC, Chris Lalancette
no flags Details | Diff

External Trackers
Tracker ID Priority Status Summary Last Updated
Red Hat Product Errata RHBA-2008:0314 normal SHIPPED_LIVE Updated kernel packages for Red Hat Enterprise Linux 5.2 2008-05-20 18:43:34 UTC

Description Chris Lalancette 2008-01-25 23:58:17 UTC
Description of problem:
When doing some performance testing, Barry noticed that running his applications
inside a 5.2 domU resulted in poor performance.  After some debugging, it was
determined that the reason his applications had poor performance is that all
processes in a domU were being pinned to vCPU 0, so scalability was tanking. 
This is not a hypervisor problem, as just changing the domU kernel from -75 back
to -53 makes the problem go away.  Bisecting kernels, it looks like -58 kernel
is fine, but -59 kernel is where the problem starts.  I'm going to start looking
at patches in the -59 kernel.

Comment 1 Bill Burns 2008-01-26 00:34:46 UTC
Setting flags

Comment 2 Chris Lalancette 2008-01-26 00:44:58 UTC
It looks like the "force /sbin/init off isolated cpus" patch is probably the
culprit here.  There is an additional upstream changeset:


That we do *not* have in the RHEL-5 kernel; this uses cpu_possible_map instead
of cpu_online_map to figure out isolated CPUs, which seems to fix the issue in
my limited testing.  I'm going to produce a real patch, then run it through brew
and get some testing on it.

Chris Lalancette

Comment 3 Chris Lalancette 2008-01-26 00:48:40 UTC
Created attachment 293025 [details]
Patch to fix the problem where init is only set to vcpu 0

Comment 4 Rik van Riel 2008-01-26 00:54:04 UTC
Barry, I think we have a winner.

Comment 5 Barry Marson 2008-01-26 01:57:00 UTC
Rik, do you want to rebuild your other test kernel with this fix ? Or is my
workaround (using taskset) enough ?


Comment 6 Rik van Riel 2008-01-26 11:03:33 UTC
Barry, the taskset workaround is good enough for you, but too easy to forget for
the folks at the SAP workshop.

I just kicked off http://brewweb.devel.redhat.com/brew/taskinfo?taskID=1134361
 and will update the kernels on my page once the build finishes.

Comment 7 Barry Marson 2008-01-27 21:24:06 UTC
I verified the patch works in Rik's kernel


Comment 10 Don Zickus 2008-01-30 17:02:04 UTC
in 2.6.18-76.el5
You can download this test kernel from http://people.redhat.com/dzickus/el5

Comment 13 errata-xmlrpc 2008-05-21 15:08:03 UTC
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on the solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.


Note You need to log in before you can comment on or make changes to this bug.