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From: Alexander Graf <agraf@suse.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org,
	tglx@linutronix.de, linux-tip-commits@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: [PATCH] sched: Remove PREEMPT_NEED_RESCHED from generic code
Date: Thu, 28 Nov 2013 16:24:45 +0100	[thread overview]
Message-ID: <5297603D.6040300@suse.de> (raw)
In-Reply-To: <20131128132641.GP10022@twins.programming.kicks-ass.net>

On 11/28/2013 02:26 PM, Peter Zijlstra wrote:
> Subject: sched: Remove PREEMPT_NEED_RESCHED from generic code
>
> While hunting a preemption issue with Alexander, Ben noticed that the
> currently generic PREEMPT_NEED_RESCHED stuff is horribly broken for
> load-store architectures.
>
> We currently rely on the IPI to fold TIF_NEED_RESCHED into
> PREEMPT_NEED_RESCHED, but when this IPI lands while we already have
> a load for the preempt-count but before the store, the store will erase
> the PREEMPT_NEED_RESCHED change.
>
> The current preempt-count only works on load-store archs because
> interrupts are assumed to be completely balanced wrt their preempt_count
> fiddling; the previous preempt_count load will match the preempt_count
> state after the interrupt and therefore nothing gets lost.
>
> This patch removes the PREEMPT_NEED_RESCHED usage from generic code and
> pushes it into x86 arch code; the generic code goes back to relying on
> TIF_NEED_RESCHED.
>
> Boot tested on x86_64 and compile tested on ppc64.
>
> Reported-by: Alexander Graf <agraf@suse.de>
> Reported-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Signed-off-by: Peter Zijlstra <peterz@infradead.org>

Fixes the issue for me.

Tested-by: Alexander Graf <agraf@suse.de>


Alex


  reply	other threads:[~2013-11-28 15:24 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-09-25 16:38 [tip:sched/core] sched: Add NEED_RESCHED to the preempt_count tip-bot for Peter Zijlstra
2013-09-27  9:14 ` Yuanhan Liu
2013-09-27 11:57   ` Peter Zijlstra
2013-09-27 12:13     ` Fengguang Wu
2013-09-27 12:20       ` Fengguang Wu
2013-09-27 15:29   ` [PATCH] ftrace, sched: Add TRACE_FLAG_PREEMPT_RESCHED Peter Zijlstra
2013-10-04  8:09     ` Peter Zijlstra
2013-10-04 14:53       ` Steven Rostedt
2013-10-04 15:16         ` Peter Zijlstra
2013-10-04 15:25           ` Steven Rostedt
2013-10-04 15:28         ` Peter Zijlstra
2013-10-04 15:57           ` Steven Rostedt
2013-10-04 16:28             ` Peter Zijlstra
2013-11-11 17:52           ` [tip:sched/core] " tip-bot for Peter Zijlstra
2013-11-06 16:37     ` [PATCH] " Steven Rostedt
2013-11-06 16:45       ` Peter Zijlstra
2013-11-06 16:58         ` Steven Rostedt
2013-11-06 17:23           ` Peter Zijlstra
2013-09-27 15:30   ` [PATCH] sched: Revert need_resched() to look at TIF_NEED_RESCHED Peter Zijlstra
2013-09-28  8:28     ` [tip:sched/core] " tip-bot for Peter Zijlstra
2013-12-09  6:41     ` [PATCH] " Aneesh Kumar K.V
2013-12-10 15:52       ` Peter Zijlstra
2013-11-28 13:26 ` [PATCH] sched: Remove PREEMPT_NEED_RESCHED from generic code Peter Zijlstra
2013-11-28 15:24   ` Alexander Graf [this message]
2013-12-09  6:29   ` Benjamin Herrenschmidt
2013-12-12  9:51   ` [tip:sched/urgent] " tip-bot for Peter Zijlstra

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