From: Peter Zijlstra <peterz@infradead.org>
To: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Peter Hurley <peter@hurleysoftware.com>,
Davidlohr Bueso <davidlohr.bueso@hp.com>,
Alex Shi <alex.shi@intel.com>,
Michel Lespinasse <walken@google.com>,
Ingo Molnar <mingo@elte.hu>,
Andrew Morton <akpm@linux-foundation.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Andi Kleen <andi@firstfloor.org>,
Matthew R Wilcox <matthew.r.wilcox@intel.com>,
Dave Hansen <dave.hansen@intel.com>,
Rik van Riel <riel@redhat.com>,
linux-kernel@vger.kernel.org, linux-mm <linux-mm@kvack.org>
Subject: Re: [PATCH 2/2] rwsem: do optimistic spinning for writer lock acquisition
Date: Tue, 25 Jun 2013 09:37:39 +0200 [thread overview]
Message-ID: <20130625073739.GX28407@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1372105065.22432.65.camel@schen9-DESK>
On Mon, Jun 24, 2013 at 01:17:45PM -0700, Tim Chen wrote:
> On second thought, I agree with you. I should change this to
> something like
>
> int retval = true;
> task_struct *sem_owner;
>
> /* Spin only if active writer running */
> if (!sem->owner)
> return false;
>
> rcu_read_lock();
> sem_owner = sem->owner;
That should be: sem_owner = ACCESS_ONCE(sem->owner); to make sure the
compiler doesn't try and be clever and rereads.
> if (sem_owner)
> retval = sem_owner->on_cpu;
>
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WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Peter Hurley <peter@hurleysoftware.com>,
Davidlohr Bueso <davidlohr.bueso@hp.com>,
Alex Shi <alex.shi@intel.com>,
Michel Lespinasse <walken@google.com>,
Ingo Molnar <mingo@elte.hu>,
Andrew Morton <akpm@linux-foundation.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Andi Kleen <andi@firstfloor.org>,
Matthew R Wilcox <matthew.r.wilcox@intel.com>,
Dave Hansen <dave.hansen@intel.com>,
Rik van Riel <riel@redhat.com>,
linux-kernel@vger.kernel.org, linux-mm <linux-mm@kvack.org>
Subject: Re: [PATCH 2/2] rwsem: do optimistic spinning for writer lock acquisition
Date: Tue, 25 Jun 2013 09:37:39 +0200 [thread overview]
Message-ID: <20130625073739.GX28407@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1372105065.22432.65.camel@schen9-DESK>
On Mon, Jun 24, 2013 at 01:17:45PM -0700, Tim Chen wrote:
> On second thought, I agree with you. I should change this to
> something like
>
> int retval = true;
> task_struct *sem_owner;
>
> /* Spin only if active writer running */
> if (!sem->owner)
> return false;
>
> rcu_read_lock();
> sem_owner = sem->owner;
That should be: sem_owner = ACCESS_ONCE(sem->owner); to make sure the
compiler doesn't try and be clever and rereads.
> if (sem_owner)
> retval = sem_owner->on_cpu;
>
next prev parent reply other threads:[~2013-06-25 7:38 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <cover.1371855277.git.tim.c.chen@linux.intel.com>
2013-06-21 23:51 ` [PATCH 1/2] rwsem: check the lock before cpmxchg in down_write_trylock and rwsem_do_wake Tim Chen
2013-06-21 23:51 ` Tim Chen
2013-06-22 0:10 ` Alex Shi
2013-06-22 0:10 ` Alex Shi
2013-06-22 0:15 ` Davidlohr Bueso
2013-06-22 0:15 ` Davidlohr Bueso
2013-06-24 16:34 ` Tim Chen
2013-06-24 16:34 ` Tim Chen
2013-06-22 7:21 ` Peter Hurley
2013-06-22 7:21 ` Peter Hurley
2013-06-23 1:16 ` Alex Shi
2013-06-23 1:16 ` Alex Shi
2013-06-23 5:10 ` Andi Kleen
2013-06-23 5:10 ` Andi Kleen
2013-06-23 11:52 ` Alex Shi
2013-06-23 11:52 ` Alex Shi
2013-06-21 23:51 ` [PATCH 2/2] rwsem: do optimistic spinning for writer lock acquisition Tim Chen
2013-06-21 23:51 ` Tim Chen
2013-06-22 0:00 ` Davidlohr Bueso
2013-06-22 0:00 ` Davidlohr Bueso
2013-06-22 7:57 ` Peter Hurley
2013-06-22 7:57 ` Peter Hurley
2013-06-23 20:03 ` Davidlohr Bueso
2013-06-23 20:03 ` Davidlohr Bueso
2013-06-24 17:11 ` Tim Chen
2013-06-24 17:11 ` Tim Chen
2013-06-24 18:49 ` Peter Hurley
2013-06-24 18:49 ` Peter Hurley
2013-06-24 19:13 ` Tim Chen
2013-06-24 19:13 ` Tim Chen
2013-06-24 20:32 ` Peter Hurley
2013-06-24 20:32 ` Peter Hurley
2013-06-24 20:17 ` Tim Chen
2013-06-24 20:17 ` Tim Chen
2013-06-24 20:48 ` Peter Hurley
2013-06-24 20:48 ` Peter Hurley
2013-06-24 21:30 ` Tim Chen
2013-06-24 21:30 ` Tim Chen
2013-06-25 7:37 ` Peter Zijlstra [this message]
2013-06-25 7:37 ` Peter Zijlstra
2013-06-25 16:00 ` Tim Chen
2013-06-25 16:00 ` Tim Chen
2013-06-24 21:58 ` Tim Chen
2013-06-24 21:58 ` Tim Chen
2013-06-24 22:08 ` Peter Hurley
2013-06-24 22:08 ` Peter Hurley
2013-06-24 8:46 ` Peter Zijlstra
2013-06-24 8:46 ` Peter Zijlstra
2013-06-24 16:36 ` Tim Chen
2013-06-24 16:36 ` Tim Chen
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