From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757541Ab3EGHvZ (ORCPT ); Tue, 7 May 2013 03:51:25 -0400 Received: from mga11.intel.com ([192.55.52.93]:60699 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756504Ab3EGHvY (ORCPT ); Tue, 7 May 2013 03:51:24 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.87,627,1363158000"; d="scan'208";a="333723339" Message-ID: <5188B272.3010207@intel.com> Date: Tue, 07 May 2013 15:51:14 +0800 From: Alex Shi User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130329 Thunderbird/17.0.5 MIME-Version: 1.0 To: Peter Zijlstra CC: mingo@redhat.com, tglx@linutronix.de, akpm@linux-foundation.org, arjan@linux.intel.com, bp@alien8.de, pjt@google.com, namhyung@kernel.org, efault@gmx.de, morten.rasmussen@arm.com, vincent.guittot@linaro.org, gregkh@linuxfoundation.org, preeti@linux.vnet.ibm.com, viresh.kumar@linaro.org, linux-kernel@vger.kernel.org, len.brown@intel.com, rafael.j.wysocki@intel.com, jkosina@suse.cz, clark.williams@gmail.com, tony.luck@intel.com, keescook@chromium.org, mgorman@suse.de, riel@redhat.com Subject: Re: [PATCH v4 0/6] sched: use runnable load based balance References: <1367040344-14485-1-git-send-email-alex.shi@intel.com> <20130501121421.GA19602@dyad.programming.kicks-ass.net> <5181B579.9000808@intel.com> <20130502103508.GA13196@dyad.programming.kicks-ass.net> <51836D74.2030409@intel.com> In-Reply-To: <51836D74.2030409@intel.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/03/2013 03:55 PM, Alex Shi wrote: > >> That should probably look like: >> >> preempt_disable(); >> raw_spin_unlock_irq(); >> preempt_enable_no_resched(); >> schedule(); >> >> Otherwise you might find a performance regression on PREEMPT=y kernels. > > Yes, right! > Thanks a lot for reminder. The following patch will fix it. >> Peter, would you like to pick this patch? > > --- > > From 4c9b4b8a9b92bcbe6934637fd33c617e73dbda97 Mon Sep 17 00:00:00 2001 > From: Alex Shi > Date: Fri, 3 May 2013 14:51:25 +0800 > Subject: [PATCH 8/8] rwsem: small optimizing rwsem_down_failed_common > > Peter Zijlstra suggest adding a preempt_enable_no_resched() to prevent > a unnecessary scheduler in raw_spin_unlock. > And we also can pack 2 raw_spin_lock to save one. So has this patch. > > Thanks Peter! > > Signed-off-by: Alex Shi > --- > lib/rwsem.c | 12 +++++++----- > 1 file changed, 7 insertions(+), 5 deletions(-) > > diff --git a/lib/rwsem.c b/lib/rwsem.c > index ad5e0df..9aacf81 100644 > --- a/lib/rwsem.c > +++ b/lib/rwsem.c > @@ -212,23 +212,25 @@ rwsem_down_failed_common(struct rw_semaphore *sem, > adjustment == -RWSEM_ACTIVE_WRITE_BIAS) > sem = __rwsem_do_wake(sem, RWSEM_WAKE_READ_OWNED); > > - raw_spin_unlock_irq(&sem->wait_lock); > - > /* wait to be given the lock */ > for (;;) { > - if (!waiter.task) > + if (!waiter.task) { > + raw_spin_unlock_irq(&sem->wait_lock); > break; > + } > > - raw_spin_lock_irq(&sem->wait_lock); > - /* Try to get the writer sem, may steal from the head writer: */ > + /* Try to get the writer sem, may steal from the head writer */ > if (flags == RWSEM_WAITING_FOR_WRITE) > if (try_get_writer_sem(sem, &waiter)) { > raw_spin_unlock_irq(&sem->wait_lock); > return sem; > } > + preempt_disable(); > raw_spin_unlock_irq(&sem->wait_lock); > + preempt_enable_no_resched(); > schedule(); > set_task_state(tsk, TASK_UNINTERRUPTIBLE); > + raw_spin_lock_irq(&sem->wait_lock); > } > > tsk->state = TASK_RUNNING; > -- Thanks Alex