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Re: [RFC PATCH v2] membarrier: expedited private command

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: [RFC PATCH v2] membarrier: expedited private command
Date 2017-07-28 18:50 +0200
Message-ID <u8gCC-6cX-3@gated-at.bofh.it> (permalink)
References <u7Ymm-2WL-29@gated-at.bofh.it> <u89hL-1q4-11@gated-at.bofh.it> <u8c5Y-3fm-7@gated-at.bofh.it> <u8fwS-5yW-11@gated-at.bofh.it>
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On Fri, Jul 28, 2017 at 03:38:15PM +0000, Mathieu Desnoyers wrote:
> > Which only leaves PPC stranded.. but the 'good' news is that mpe says
> > they'll probably need a barrier in switch_mm() in any case.
> 
> As I pointed out in my other email, I plan to do this:
> 
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2636,6 +2636,11 @@ static struct rq *finish_task_switch(struct task_struct *prev)
>         vtime_task_switch(prev);
>         perf_event_task_sched_in(prev, current);

Here would place it _inside_ the rq->lock, which seems to make more
sense given the purpose of the barrier, but either way works given its
definition.

>         finish_lock_switch(rq, prev);

You could put the whole thing inside IS_ENABLED(CONFIG_SYSMEMBARRIER) or
something.

> +       /*
> +        * The membarrier system call requires a full memory barrier
> +        * after storing to rq->curr, before going back to user-space.
> +        */
> +       smp_mb__after_unlock_lock();
>         finish_arch_post_lock_switch();
>  
>         fire_sched_in_preempt_notifiers(current);

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[RFC PATCH v2] membarrier: expedited private command Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2017-07-27 23:20 +0200
  Re: [RFC PATCH v2] membarrier: expedited private command "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-28 00:20 +0200
    Re: [RFC PATCH v2] membarrier: expedited private command Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2017-07-28 00:40 +0200
      Re: [RFC PATCH v2] membarrier: expedited private command "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-07-28 01:00 +0200
  Re: [RFC PATCH v2] membarrier: expedited private command Peter Zijlstra <peterz@infradead.org> - 2017-07-28 11:00 +0200
    Re: [RFC PATCH v2] membarrier: expedited private command Peter Zijlstra <peterz@infradead.org> - 2017-07-28 13:20 +0200
    Re: [RFC PATCH v2] membarrier: expedited private command Peter Zijlstra <peterz@infradead.org> - 2017-07-28 14:00 +0200
      Re: [RFC PATCH v2] membarrier: expedited private command Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2017-07-28 17:40 +0200
        Re: [RFC PATCH v2] membarrier: expedited private command Peter Zijlstra <peterz@infradead.org> - 2017-07-28 18:50 +0200
          Re: [RFC PATCH v2] membarrier: expedited private command Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2017-07-28 19:10 +0200
            Re: [RFC PATCH v2] membarrier: expedited private command Nicholas Piggin <npiggin@gmail.com> - 2017-07-29 04:00 +0200
              Re: [RFC PATCH v2] membarrier: expedited private command Peter Zijlstra <peterz@infradead.org> - 2017-07-29 11:30 +0200
                Re: [RFC PATCH v2] membarrier: expedited private command Nicholas Piggin <npiggin@gmail.com> - 2017-07-29 11:50 +0200
                Re: [RFC PATCH v2] membarrier: expedited private command Peter Zijlstra <peterz@infradead.org> - 2017-07-29 13:00 +0200
                Re: [RFC PATCH v2] membarrier: expedited private command Nicholas Piggin <npiggin@gmail.com> - 2017-07-29 11:50 +0200
    Re: [RFC PATCH v2] membarrier: expedited private command Mathieu Desnoyers <mathieu.desnoyers@efficios.com> - 2017-07-28 17:40 +0200

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