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 S933034AbcBIVqn (ORCPT <rfc822;w@1wt.eu>);
	Tue, 9 Feb 2016 16:46:43 -0500
Received: from g2t4625.austin.hp.com ([15.73.212.76]:38207 "EHLO
	g2t4625.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S932512AbcBIVqm (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 9 Feb 2016 16:46:42 -0500
Message-ID: <1455054274.2976.31.camel@j-VirtualBox>
Subject: Re: [PATCH 0/2] locking/mutex: Enable optimistic spinning of lock
 waiter
From: Jason Low <jason.low2@hp.com>
To: Waiman Long <Waiman.Long@hpe.com>
Cc: Ingo Molnar <mingo@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
        linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Ding Tianhong <dingtianhong@huawei.com>,
        Jason Low <jason.low2@hpe.com>, Davidlohr Bueso <dave@stgolabs.net>,
        "Paul E. McKenney" <paulmck@us.ibm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Will Deacon <Will.Deacon@arm.com>,
        Tim Chen <tim.c.chen@linux.intel.com>, jason.low2@hpe.com
Date: Tue, 09 Feb 2016 13:44:34 -0800
In-Reply-To: <1455047262-27731-1-git-send-email-Waiman.Long@hpe.com>
References: <1455047262-27731-1-git-send-email-Waiman.Long@hpe.com>
Content-Type: text/plain; charset="UTF-8"
X-Mailer: Evolution 3.10.4-0ubuntu2 
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 Tue, 2016-02-09 at 14:47 -0500, Waiman Long wrote:
> This patchset is a variant of PeterZ's "locking/mutex: Avoid spinner
> vs waiter starvation" patch. The major difference is that the
> waiter-spinner won't enter into the OSQ used by the spinners. Instead,
> it will spin directly on the lock in parallel with the queue head
> of the OSQ. So there will be a bit more cacheline contention on the
> lock cacheline, but that shouldn't cause noticeable impact on system
> performance.
> 
> This patchset tries to address 2 issues with Peter's patch:
> 
>  1) Ding Tianhong still find that hanging task could happen in some cases.
>  2) Jason Low found that there was performance regression for some AIM7
>     workloads.

This might help address the hang that Ding reported.

Performance wise, this patchset reduced AIM7 fserver throughput on the 8
socket machine by -70%+ at 1000+ users.

                | fserver JPM
-----------------------------
baseline	| ~450000
Peter's patch	| ~410000
This patchset	| ~100000

My guess is that waiters spinning/acquiring the lock is less efficient,
and this patchset further increases the chance for waiters to
spin/acquire the lock over the fastpath optimistic spinners.

Jason