Messages in this thread | | | Date | Fri, 11 Feb 2011 14:36:18 +0100 | Subject | Re: [PATCH 1/2] perf_events: add cgroup support (v8) | From | Stephane Eranian <> |
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On Fri, Feb 11, 2011 at 10:56 AM, Stephane Eranian <eranian@google.com> wrote: > Li, > > On Fri, Feb 11, 2011 at 1:55 AM, Li Zefan <lizf@cn.fujitsu.com> wrote: >>>>> while there is already cgroup monitoring active. In that case and if we do not >>>>> want to wait until there is at least one ctxsw on all CPUs, then we have to >>>>> check if the other threads are not already running on the other CPUs.If so, >>>>> we need to do a cgroup switch on those CPUs. Otherwise, we have nothing to >>>>> do. Am I getting this right? >>>> >>>> Right, so if any of those tasks is currently running, that cpu will be >>>> monitoring their old cgroup, hence we send an IPI to flip cgroups. >>>> >>> I have built a test case where this would trigger. I launched a multi-threaded >>> app, and then I move the pid into a cgroup via: echo PID >/cgroup/tests/tasks. >>> I don't see any perf_cgroup move beyond the PID passed. >>> >>> I looked at kernel/cgroup.c and I could not find a invocation of >>> ss->attach() that >>> would pass threadgroup = true. So I am confused here. >>> >>> I wonder how the cgroupfs 'echo PID >tasks' interface would make the distinction >>> between PID and TID. It seems possible to move one thread of a multi-threaded >>> process into a cgroup but not the others. >>> >> >> You can do this: >> >> # echo PID > cgroup.procs >> >> When the patchset that implements the above feature is accepted. See: >> >> https://lkml.org/lkml/2011/2/7/418 >> >> The below commit that confused you is actually a part of the above patchset, >> but it sneaked into the kernel accidentally: >> >> commit be367d09927023d081f9199665c8500f69f14d22 >> Author: Ben Blum <bblum@google.com> >> Date: Wed Sep 23 15:56:31 2009 -0700 >> >> cgroups: let ss->can_attach and ss->attach do whole threadgroups at a time >> > Ok, that makes more sense now. I wil try with the above patchset applied to > verify this work as expected. > The above patchset seems to work fine. I add to switch perf_event from ss->attach() to ss->attach_task() to make it work with multi-threaded apps. The good thing is that it simplifies the code, because all we have to do now is simply call perf_cgroup_move(). The caller does the thread iteration.
During this exercise, I found a minor issue in event_sched_out() with the current perf cgroup patch. I will resubmit the patch incl. Peter's changes + some more cleanups and the fix + the update perf cgroup patch.
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