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 S1752560AbbGBJmK (ORCPT <rfc822;w@1wt.eu>);
	Thu, 2 Jul 2015 05:42:10 -0400
Received: from casper.infradead.org ([85.118.1.10]:44895 "EHLO
	casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751918AbbGBJmC (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Thu, 2 Jul 2015 05:42:02 -0400
Date: Thu, 2 Jul 2015 11:41:55 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Daniel Wagner <wagi@monom.org>, Ingo Molnar <mingo@kernel.org>,
        Oleg Nesterov <oleg@redhat.com>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>, Tejun Heo <tj@kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        der.herr@hofr.at, Davidlohr Bueso <dave@stgolabs.net>,
        Rik van Riel <riel@redhat.com>, Al Viro <viro@zeniv.linux.org.uk>,
        Jeff Layton <jlayton@poochiereds.net>
Subject: Re: [RFC][PATCH 00/13] percpu rwsem -v2
Message-ID: <20150702094155.GW19282@twins.programming.kicks-ass.net>
References: <20150622190553.GZ3644@twins.programming.kicks-ass.net>
 <5589285C.2010100@bmw-carit.de>
 <20150623143411.GA25159@twins.programming.kicks-ass.net>
 <558973A7.6010407@bmw-carit.de>
 <20150623175012.GD3644@twins.programming.kicks-ass.net>
 <20150623193624.GH18673@twins.programming.kicks-ass.net>
 <20150624084648.GB27873@gmail.com>
 <558A75EA.40905@bmw-carit.de>
 <55938163.7020606@monom.org>
 <CA+55aFy0nKSbr6YRUV62Ns9E53yJ9Wf1KHd2+mh+G12Co-tsiA@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CA+55aFy0nKSbr6YRUV62Ns9E53yJ9Wf1KHd2+mh+G12Co-tsiA@mail.gmail.com>
User-Agent: Mutt/1.5.21 (2012-12-30)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, Jul 01, 2015 at 02:54:59PM -0700, Linus Torvalds wrote:
> On Tue, Jun 30, 2015 at 10:57 PM, Daniel Wagner <wagi@monom.org> wrote:
> >
> > And an attempt at visualization:
> >
> > http://monom.org/posix01/sweep-4.1.0-02756-ge3d06bd.png
> > http://monom.org/posix01/sweep-4.1.0-02769-g6ce2591.png
> 
> Ugh. The old numbers look (mostly) fairly tight, and then the new ones
> are all over the map, and usually much worse.
> 
> We've seen this behavior before when switching from a non-sleeping
> lock to a sleeping one. The sleeping locks have absolutely horrible
> behavior when they get contended, and spend tons of CPU time on the
> sleep/wakeup management, 

Right, I'm just not seeing how any of that would happen here :/ The read
side would only ever block on reading /proc/$something and I'm fairly
sure that benchmark doesn't actually touch that file.

In any case, I will look into this, I've just not had time yet..