On 2016-09-12 08:05 PM, Rafael J. Wysocki wrote:

On Monday, September 12, 2016 11:15:45 PM Rafael J. Wysocki wrote:

quoted

On Monday, September 12, 2016 06:14:44 PM Peter Zijlstra wrote:

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On Mon, Sep 12, 2016 at 12:01:58PM -0400, Chris Metcalf wrote:

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On 9/7/2016 5:11 PM, Francis Giraldeau wrote:

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When running only the test_jitter(), the isolation mode is lost:

    [ 6741.566048] isolation/9515: task_isolation mode lost due to irq_work

With ftrace (events/workqueue/workqueue_execute_start), I get a bit more info:

     kworker/1:1-676   [001] ....  6610.097128: workqueue_execute_start: work struct ffff8801a784ca20: function dbs_work_handler

The governor was ondemand, so I tried to set the frequency scaling
governor to performance, but that does not solve the issue.

Rafael, I'm thinking the performance governor should be able to run
without sending IPIs. Is there anything we can quickly do about that?

The performance governor doesn't do any IPIs.

At this point I'm not sure what's going on.

I've just tried and switching over to the performance governor makes
dbs_work_handler go away for me (w/ -rc4 with some extra irrelevant patches
on top) as it should.

Ho gosh, the command "cpufreq-set -g performance" sets the governor only
for cpu0. I was expecting it to set for all cpus. The isolation test runs
on cpu1 and this cpu was still with ondemand governor. With performance
governor, the dbs_work_handler does not occurs anymore and the isolated
task is not preempted by that kworker thread anymore.

Sorry for the noise and thanks for checking!

Francis