From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752211Ab1FNNTV (ORCPT ); Tue, 14 Jun 2011 09:19:21 -0400 Received: from casper.infradead.org ([85.118.1.10]:39417 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751215Ab1FNNTS convert rfc822-to-8bit (ORCPT ); Tue, 14 Jun 2011 09:19:18 -0400 Subject: Re: rcu: performance regression From: Peter Zijlstra To: paulmck@linux.vnet.ibm.com Cc: "Alex,Shi" , "Li, Shaohua" , Ingo Molnar , lkml , "Chen, Tim C" , rostedt@goodmis.org In-Reply-To: <1308057298.19856.40.camel@twins> References: <1308029185.15392.147.camel@sli10-conroe> <1308040388.21027.1847.camel@debian> <20110614130203.GF2264@linux.vnet.ibm.com> <1308057298.19856.40.camel@twins> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Tue, 14 Jun 2011 15:18:42 +0200 Message-ID: <1308057522.19856.41.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2011-06-14 at 15:14 +0200, Peter Zijlstra wrote: > On Tue, 2011-06-14 at 06:02 -0700, Paul E. McKenney wrote: > > > This commit also cause hackbench process mode performance dropping, and > > > Shaohua's patch do recovered this. But in hackbench testing, the vmstat > > > show context switch have some reduce. And perf tool show > > > root_domain->cpupri->prio_to_cpu[]->lock has contention with the commit. > > > > Steven, Peter, would any of the recent fixes address this lock contention? > > No. People occasionally run into that thing, but given the constraints > on SCHED_FIFO SMP (run the n highest priority tasks on m cpus; n<=m) > there isn't really much we can do. > > IIRC Chris Mason once proposed a lockless version, but that opened up > race windows, Steve might know the details better. Note that even a lockless version will die of cacheline contention.