Hi Daniel,

On 19/09/14 12:47, Daniel Wagner wrote:

Hi,

On 09/19/2014 11:22 AM, Juri Lelli wrote:

quoted

Exclusive cpusets are the only way users can restrict SCHED_DEADLINE tasks
affinity (performing what is commonly called clustered scheduling).
Unfortunately, such thing is currently broken for two reasons:

 - No check is performed when the user tries to attach a task to
   an exlusive cpuset (recall that exclusive cpusets have an
   associated maximum allowed bandwidth).

 - Bandwidths of source and destination cpusets are not correctly
   updated after a task is migrated between them.

This patch fixes both things at once, as they are opposite faces
of the same coin.

The check is performed in cpuset_can_attach(), as there aren't any
points of failure after that function. The updated is split in two
halves. We first reserve bandwidth in the destination cpuset, after
we pass the check in cpuset_can_attach(). And we then release
bandwidth from the source cpuset when the task's affinity is
actually changed. Even if there can be time windows when sched_setattr()
may erroneously fail in the source cpuset, we are fine with it, as
we can't perfom an atomic update of both cpusets at once.

Reported-by: Daniel Wagner <redacted>

Ack

I have no special test for this, I just let my test running which was
fixed by patch #1. Works fine though. I'll plan to write some test for this.

Ok, thanks. Just mind that the problem fixed by patch 3/3 may sometime
affect this too. I should have definitely put 3/3 on top of the patchset :/.

Thanks,

- Juri