Messages in this thread | | | Date | Wed, 15 Apr 2015 15:32:11 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 2/3] sched, timer: Use atomics for thread_group_cputimer to improve scalability |
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On Wed, Apr 15, 2015 at 03:25:36PM +0200, Frederic Weisbecker wrote: > On Tue, Apr 14, 2015 at 04:09:45PM -0700, Jason Low wrote: > > void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times) > > { > > struct thread_group_cputimer *cputimer = &tsk->signal->cputimer; > > struct task_cputime sum; > > > > if (!cputimer->running) { > > /* > > * The POSIX timer interface allows for absolute time expiry > > * values through the TIMER_ABSTIME flag, therefore we have > > + * to synchronize the timer to the clock every time we start it. > > */ > > thread_group_cputime(tsk, &sum); > > + update_gt_cputime(cputimer, &sum); > > + /* Start 'running' after update_gt_cputime() */ > > + smp_store_release(&cputimer->running, 1); > > This barrier should be mirrored somewhere but I can't see where in this patch. > Maybe in another one in the series. Or maybe there is already a barrier in the > existing code that I'm missing. I would expect to see it in account_group_*_time(). > In any case, there should be comment about what it mirrors.
I think it should be in cputimer_running(), which should use smp_load_acquire() to read cputimer->running.
That way you guarantee that everything observing 'running' will indeed observe the initialized state.
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