From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1754711Ab3LUCeU (ORCPT <rfc822;w@1wt.eu>);
	Fri, 20 Dec 2013 21:34:20 -0500
Received: from mga02.intel.com ([134.134.136.20]:57395 "EHLO mga02.intel.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1752629Ab3LUCeT (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Fri, 20 Dec 2013 21:34:19 -0500
X-ExtLoop1: 1
X-IronPort-AV: E=Sophos;i="4.95,525,1384329600"; 
   d="scan'208";a="428127138"
Message-ID: <1387593256.3510.181.camel@dvhart-mobl4.amr.corp.intel.com>
Subject: Re: [PATCH v3 4/4] futex: Avoid taking hb lock if nothing to wakeup
From: Darren Hart <dvhart@linux.intel.com>
To: Davidlohr Bueso <davidlohr@hp.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>,
        Mike Galbraith <efault@gmx.de>, Jeff Mahoney <jeffm@suse.com>,
        Jason Low <jason.low2@hp.com>, Waiman Long <Waiman.Long@hp.com>,
        Tom Vaden <tom.vaden@hp.com>, "Norton, Scott J" <scott.norton@hp.com>,
        "Chandramouleeswaran, Aswin" <aswin@hp.com>,
        Ingo Molnar <mingo@kernel.org>
Date: Fri, 20 Dec 2013 18:34:16 -0800
In-Reply-To: <1387589770.3119.2.camel@buesod1.americas.hpqcorp.net>
References: <1387478746-5436-1-git-send-email-davidlohr@hp.com>
	 <1387478746-5436-5-git-send-email-davidlohr@hp.com>
	 <CA+55aFxY_sMes2=0tz0qTKH5-fpAaLji_xd9CdU-u2JxxNN6pA@mail.gmail.com>
	 <1387589770.3119.2.camel@buesod1.americas.hpqcorp.net>
Organization: Intel
Content-Type: text/plain; charset="UTF-8"
X-Mailer: Evolution 3.8.5 (3.8.5-2.fc19) 
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Fri, 2013-12-20 at 17:36 -0800, Davidlohr Bueso wrote:
> On Thu, 2013-12-19 at 15:14 -0800, Linus Torvalds wrote:
> > On Thu, Dec 19, 2013 at 10:45 AM, Davidlohr Bueso <davidlohr@hp.com> wrote:
> > >
> > > - increment the counter at queue_lock() as we always end up calling
> > >   queue_me() which adds the element to the list. Upon any error,
> > >   queue_unlock() is called for housekeeping, for which we decrement
> > >   to mach the increment done in queue_lock().
> > >
> > > - decrement the counter at __unqueue_me() to reflect when an element is
> > >   removed from the queue for wakeup related purposes.
> > 
> > I still hate this whole separate counter thing. It seems really annoying.
> > 
> > If re-ordering things didn't work out, then why can't just the counter
> > we *already* have in the spinlock itself work as the counter? Your
> > counter update logic seems to basically match when you take the
> > spinlock anyway.
> 
> So the following has passed all testing, just like the atomics variant.
> Thoughts?

Do you have similar performance numbers for comparison? I presume they
were *very* similar to the atomics version - I think you hinted at that
in a previous post?


-- 
Darren Hart
Intel Open Source Technology Center
Yocto Project - Linux Kernel