From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752131Ab3AaMXF (ORCPT ); Thu, 31 Jan 2013 07:23:05 -0500 Received: from mga14.intel.com ([143.182.124.37]:60202 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751295Ab3AaMXD (ORCPT ); Thu, 31 Jan 2013 07:23:03 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.84,576,1355126400"; d="scan'208";a="197042626" Date: Thu, 31 Jan 2013 20:23:54 +0800 From: Yuanhan Liu To: Ingo Molnar Cc: linux-kernel@vger.kernel.org, David Howells , Linus Torvalds , Andrew Morton , Thomas Gleixner , Peter Zijlstra , Steven Rostedt Subject: Re: [PATCH] rwsem-spinlock: let rwsem write lock stealable Message-ID: <20130131122354.GZ12678@yliu-dev.sh.intel.com> References: <1359537244-20588-1-git-send-email-yuanhan.liu@linux.intel.com> <20130131093931.GA398@gmail.com> <20130131100927.GY12678@yliu-dev.sh.intel.com> <20130131104541.GA2291@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130131104541.GA2291@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 31, 2013 at 11:45:41AM +0100, Ingo Molnar wrote: > > * Yuanhan Liu wrote: > > > > > output with this patch: > > > > ----------------------- > > > > cpu 00: 0 0 ... 1 1 2 1 1 1 2 1 1 1 .... 1 3 > > > > cpu 01: 0 0 ... 1 1 1 1 1 1 2 1 1 1 .... 1 3 > > > > cpu 02: 0 0 ... 2 2 3 2 0 2 1 2 1 1 .... 1 1 > > > > cpu 03: 0 0 ... 2 2 3 2 1 2 1 2 1 1 .... 1 1 > > > > cpu 04: 0 1 ... 2 0 0 1 0 1 3 1 1 1 .... 1 1 > > > > cpu 05: 0 1 ... 2 0 1 1 0 1 2 1 1 1 .... 1 1 > > > > cpu 06: 0 0 ... 2 1 1 2 0 1 2 1 1 1 .... 2 1 > > > > cpu 07: 0 0 ... 2 1 1 2 0 1 2 1 1 1 .... 2 1 > > > > cpu 08: 0 0 ... 1 1 1 1 1 1 1 1 1 1 .... 0 0 > > > > cpu 09: 0 0 ... 1 1 1 1 1 1 1 1 1 1 .... 0 0 > > > > cpu 10: 0 0 ... 1 1 1 0 0 1 1 1 1 1 .... 0 0 > > > > cpu 11: 0 0 ... 1 1 1 0 0 1 1 1 1 2 .... 1 0 > > > > cpu 12: 0 0 ... 1 1 1 0 1 1 0 0 0 1 .... 2 1 > > > > cpu 13: 0 0 ... 1 1 1 0 1 1 1 0 1 2 .... 2 0 > > > > cpu 14: 0 0 ... 2 0 0 0 0 1 1 1 1 1 .... 2 2 > > > > cpu 15: 0 0 ... 2 0 0 1 0 1 1 1 1 1 .... 2 2 > > > > ------------------------------------------------------------------------ > > > > Where you can see that CPU is much busier with this patch. > > > > > > That looks really good - quite similar to how it behaved > > > with mutexes, right? > > > > Yes :) > > > > And the result is almost same with mutex lock when MUTEX_SPIN_ON_OWNER > > is disabled, and that's the reason you will see massive processes(about > > 100) queued on each CPU in my last report: > > https://lkml.org/lkml/2013/1/29/84 > > Just curious: how does MUTEX_SPIN_ON_OWNER versus > !MUTEX_SPIN_ON_OWNER compare, for this particular, > massively-contended anon-vma locks benchmark? In above testcase, MUTEX_SPIN_ON_OWNER is slightly doing better job(like 3% ~ 4%) than !MUTEX_SPIN_ON_OWNER. > > > > Does this recover most of the performance regression? > > > > Yes, there is only a 10% gap here then. I guess that's because Sorry, to be accurate, it's about 14% gap; when MUTEX_SPIN_ON_OWNER is enabled. > > I used the general rwsem lock > > implementation(lib/rwsem-spinlock.c), but not the XADD > > one(lib/rwsem.c). I guess the gap may be a little smaller if > > we do the same thing to lib/rwsem.c. > > Is part of the gap due to MUTEX_SPIN_ON_OWNER perhaps? Nope, !MUTEX_SPIN_ON_OWNER does introduce a little performance drop just as above stated. So, to make it clear, here is the list: lock case performance drop compared to mutex lock ---------------------------------------------------------------------------- mutex lock w/o MUTEX_SPIN_ON_OWNER 3.x% rwsem-spinlock with write stealing 14.x% rwsem-spinlock >100% > > I'm surprised that rwsem-spinlock versus rwsem.c would show a > 10% performance difference - Yes, it may not. And there is only about 0.9% performance difference in above test between rwsem-spinlock and XADD rwsem. The difference maybe enlarged when both has write lock stealing enabled, which will be known only after we do same thing to lib/rwsem.c. Thanks. --yliu > assuming you have lock > debugging/tracing disabled in the .config. > > ( Once the performance regression is fixed, another thing to > check would be to reduce anon-vma lock contention. ) > > Thanks, > > Ingo