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From: Peter Zijlstra <peterz@infradead.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 3/4] sched: Pull preemption disablement to __schedule() caller
Date: Wed, 4 Feb 2015 18:48:45 +0100	[thread overview]
Message-ID: <20150204174845.GE5029@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20150204173152.GA24000@lerouge>

On Wed, Feb 04, 2015 at 06:31:57PM +0100, Frederic Weisbecker wrote:

> > In any case; if we make __schedule() noinline (I think that might make
> > sense) that function call would itself imply the compiler barrier and
> > something like:
> > 
> > 	__preempt_count_add(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);
> > 	__schedule();
> > 	__preempt_count_sub(PREEMPT_ACTIVE + PREEMPT_CHECK_OFFSET);
> > 
> > Would actually be safe/correct.
> > 
> > As it stands I think __schedule() would fail the GCC inline static
> > criteria for being too large, but you never know, noinline guarantees it
> > will not.
> 
> Right, although relying only on __schedule() as a function call is perhaps
> error-prone in case we add things in preempt_schedule*() APIs later, before
> the call to __schedule(), that need the preempt count to be visible.
> 
> I can create preempt_active_enter() / preempt_active_exit() that take care
> of the preempt op and the barrier() for example.

Sure, like that exception_enter() in preempt_schedule_context() for
instance?

  reply	other threads:[~2015-02-04 17:48 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-28  0:24 [PATCH 0/4] sched: schedule/preempt optimizations and cleanups Frederic Weisbecker
2015-01-28  0:24 ` [PATCH 1/4] sched: Pull resched loop to __schedule() callers Frederic Weisbecker
2015-02-04 14:36   ` [tip:sched/core] " tip-bot for Frederic Weisbecker
2015-01-28  0:24 ` [RFC PATCH 2/4] sched: Use traced preempt count operations to toggle PREEMPT_ACTIVE Frederic Weisbecker
2015-01-28  1:42   ` Steven Rostedt
2015-01-28 13:59     ` Frederic Weisbecker
2015-01-28 15:04       ` Steven Rostedt
2015-01-28 15:42   ` Peter Zijlstra
2015-02-02 17:22     ` Frederic Weisbecker
2015-01-28  0:24 ` [PATCH 3/4] sched: Pull preemption disablement to __schedule() caller Frederic Weisbecker
2015-01-28 15:50   ` Peter Zijlstra
2015-02-02 17:53     ` Frederic Weisbecker
2015-02-03 10:53       ` Peter Zijlstra
2015-02-04 17:31         ` Frederic Weisbecker
2015-02-04 17:48           ` Peter Zijlstra [this message]
2015-01-28  0:24 ` [RFC PATCH 4/4] sched: Account PREEMPT_ACTIVE context as atomic Frederic Weisbecker
2015-01-28 15:46   ` Peter Zijlstra
2015-02-02 17:29     ` Frederic Weisbecker

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