Hi Peter, On 19/09/14 22:25, Peter Zijlstra wrote: > 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. > Right, next week I should be able to properly test this. Thanks a lot, - Juri -- 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
