Messages in this thread | | | From | Paul Menage <> | Date | Mon, 7 Feb 2011 11:29:08 -0800 | Subject | Re: [PATCH 1/2] perf_events: add cgroup support (v8) |
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On Wed, Feb 2, 2011 at 4:46 AM, Peter Zijlstra <peterz@infradead.org> wrote: > On Wed, 2011-02-02 at 17:20 +0530, Balbir Singh wrote: >> * Peter Zijlstra <peterz@infradead.org> [2011-02-02 12:29:20]: >> >> > On Thu, 2011-01-20 at 15:39 +0100, Peter Zijlstra wrote: >> > > On Thu, 2011-01-20 at 15:30 +0200, Stephane Eranian wrote: >> > > > @@ -4259,8 +4261,20 @@ void cgroup_exit(struct task_struct *tsk, int run_callbacks) >> > > > >> > > > /* Reassign the task to the init_css_set. */ >> > > > task_lock(tsk); >> > > > + /* >> > > > + * we mask interrupts to prevent: >> > > > + * - timer tick to cause event rotation which >> > > > + * could schedule back in cgroup events after >> > > > + * they were switched out by perf_cgroup_sched_out() >> > > > + * >> > > > + * - preemption which could schedule back in cgroup events >> > > > + */ >> > > > + local_irq_save(flags); >> > > > + perf_cgroup_sched_out(tsk); >> > > > cg = tsk->cgroups; >> > > > tsk->cgroups = &init_css_set; >> > > > + perf_cgroup_sched_in(tsk); >> > > > + local_irq_restore(flags); >> > > > task_unlock(tsk); >> > > > if (cg) >> > > > put_css_set_taskexit(cg); >> > > >> > > So you too need a callback on cgroup change there.. Li, Paul, any chance >> > > we can fix this cgroup_subsys::exit callback? The scheduler code needs >> > > to do funny thing because its in the wrong place as well. >> > >> > cgroup guys? Shall I just fix this exit thing since the only user seems >> > to be the scheduler and now perf for both of which its unfortunate at >> > best? >> >> Are you suggesting that the cgroup_exit on task_exit notification should be >> pulled out? > > > No, just fixed. The callback as it exists isn't useful and leads to > hacks like the above. > > >> > Balbir, memcontrol.c uses pre_destroy(), I pose that using this method >> > is broken per definition since it makes the cgroup empty notification >> > void. >> > >> >> We use pre_destroy() to reclaim, so that delete/rmdir() will be able >> to clean up the node/group. I am not sure what you mean by it makes >> the empty notification void and why pre_destroy() is broken? > > A quick look at the code looked like it could return -EBUSY (and other > errors), in that case the rmdir of the empty cgroup will fail. > > Therefore it can happen that after the last task is removed, and we get > the notification that the cgroup is empty, and we attempt the rmdir we > will fail. > > This again means that all such notification handlers must poll state, > which is ridiculous. >
Not necessarily - we could make it that a failed rmdir() sets a bit that causes a notification again once the final refcount is dropped again on the cgroup.
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