Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753674Ab1E0HBk (ORCPT ); Fri, 27 May 2011 03:01:40 -0400 Received: from mail-yx0-f174.google.com ([209.85.213.174]:59276 "EHLO mail-yx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751306Ab1E0HBi convert rfc822-to-8bit (ORCPT ); Fri, 27 May 2011 03:01:38 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=Xz+18zZLtBkIWU53IAxldViNhAmW7yQaQ6lvcmKxqOKcK+c6La6k94v1Q+AB127hT6 +3GDEgFzHr5kSvLQ4ak0v8fv89n3TKSPtlagR8Wq0JJXbjKI6cyFC6/wkCO+ctC4oewC s/02f0gk9uBvupM6NnjbSckcfPy0RUXv9s7Co= MIME-Version: 1.0 In-Reply-To: <1306430633.2497.91.camel@laptop> References: <1306343335.21578.65.camel@twins> <1306358128.21578.107.camel@twins> <1306405979.1200.63.camel@twins> <1306407759.27474.207.camel@e102391-lin.cambridge.arm.com> <1306409575.1200.71.camel@twins> <1306412511.1200.90.camel@twins> <20110526154508.GA13788@redhat.com> <1306425584.2497.81.camel@laptop> <1306426148.2497.83.camel@laptop> <20110526170422.GA18413@redhat.com> <1306430264.2497.88.camel@laptop> <1306430633.2497.91.camel@laptop> Date: Fri, 27 May 2011 15:01:38 +0800 Message-ID: Subject: Re: [BUG] "sched: Remove rq->lock from the first half of ttwu()" locks up on ARM From: Yong Zhang To: Peter Zijlstra Cc: Oleg Nesterov , Marc Zyngier , Ingo Molnar , Frank Rowand , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3694 Lines: 99 On Fri, May 27, 2011 at 1:23 AM, Peter Zijlstra wrote: > > We'd end up with something like the below, which isn't too different > from what I've now got queued. > > It has the extra cpu == smp_processor_id() check, but I'm not sure this > whole case is worth the trouble. I could go stick some counters in to > verify how often all this happens I guess. > > --- >  arch/x86/include/asm/system.h |    2 ++ >  kernel/sched.c                |   14 +++++++++++--- >  kernel/sched_debug.c          |    7 +++++++ >  3 files changed, 20 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/include/asm/system.h b/arch/x86/include/asm/system.h > index c2ff2a1..2c597e8 100644 > --- a/arch/x86/include/asm/system.h > +++ b/arch/x86/include/asm/system.h > @@ -10,6 +10,8 @@ >  #include >  #include > > +#define __ARCH_WANT_INTERRUPTS_ON_CTXSW > + >  /* entries in ARCH_DLINFO: */ >  #if defined(CONFIG_IA32_EMULATION) || !defined(CONFIG_X86_64) >  # define AT_VECTOR_SIZE_ARCH 2 > diff --git a/kernel/sched.c b/kernel/sched.c > index 2d12893..e4f7a9f 100644 > --- a/kernel/sched.c > +++ b/kernel/sched.c > @@ -2636,9 +2636,17 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) >                 * to spin on ->on_cpu if p is current, since that would >                 * deadlock. >                 */ > -               if (p == current) { > -                       ttwu_queue(p, cpu); > -                       goto stat; > +               if (cpu == smp_processor_id()) { > +                       struct rq *rq; > + > +                       rq = __task_rq_lock(p); > +                       if (p->on_cpu) { As Oleg has said, I also think we don't need this check. > +                               ttwu_activate(rq, p, ENQUEUE_WAKEUP); > +                               ttwu_do_wakeup(rq, p, wake_flags); And the difference with ttwu_queue() is ttwu_queue() calls ttwu_activate() with another flag ENQUEUE_WAKING, so if we call ->task_waking() before ttwu_queue(), I guess it will work too. But I like this version, because we call ->task_waking() and ttwu_activate() on the local cpu, that means the calculations on vruntime in that two functions are accumulated into noop. Thanks, Yong > +                               __task_rq_unlock(rq); > +                               goto stat; > +                       } > +                       __task_rq_unlock(rq); >                } >  #endif >                cpu_relax(); > diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c > index a6710a1..f0ff1de 100644 > --- a/kernel/sched_debug.c > +++ b/kernel/sched_debug.c > @@ -332,6 +332,13 @@ static int sched_debug_show(struct seq_file *m, void *v) >                (int)strcspn(init_utsname()->version, " "), >                init_utsname()->version); > > +#ifdef __ARCH_WANT_INTERRUPTS_ON_CTXSW > +       SEQ_printf(m, "__ARCH_WANT_INTERRUPTS_ON_CTXSW\n"); > +#endif > +#ifdef __ARCH_WANT_UNLOCKED_CTXSW > +       SEQ_printf(m, "__ARCH_WANT_UNLOCKED_CTXSW\n"); > +#endif > + >  #define P(x) \ >        SEQ_printf(m, "%-40s: %Ld\n", #x, (long long)(x)) >  #define PN(x) \ > > > -- Only stand for myself -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/