On Fri, Sep 19, 2014 at 10:22:40AM +0100, Juri Lelli wrote: > 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. The thing I cannot find is if we correctly deal with updates to the cpuset. Say we first setup 2 (exclusive) sets A:cpu0 B:cpu1-3. Then assign tasks and then update the cpu masks like: B:cpu2,3, A:cpu1,2. -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
