From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757834AbZE2JQY (ORCPT ); Fri, 29 May 2009 05:16:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756475AbZE2JQR (ORCPT ); Fri, 29 May 2009 05:16:17 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:50403 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751047AbZE2JQQ (ORCPT ); Fri, 29 May 2009 05:16:16 -0400 Date: Fri, 29 May 2009 11:16:08 +0200 From: Ingo Molnar To: Peter Zijlstra Cc: Paul Mackerras , linux-kernel@vger.kernel.org Subject: Re: [PATCH RFC] perf_counter: Don't swap contexts containing locked mutex Message-ID: <20090529091608.GA15278@elte.hu> References: <18975.31580.520676.619896@drongo.ozlabs.ibm.com> <1243584388.23657.156.camel@twins> <1243584793.23657.168.camel@twins> <1243585721.23657.177.camel@twins> <20090529085916.GA21461@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090529085916.GA21461@elte.hu> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Ingo Molnar wrote: > > * Peter Zijlstra wrote: > > > On Fri, 2009-05-29 at 10:13 +0200, Peter Zijlstra wrote: > > > On Fri, 2009-05-29 at 10:06 +0200, Peter Zijlstra wrote: > > > > > > > static struct perf_counter_ctx *pin_ctx(struct perf_counter *counter, u64 *old_gen) > > > > { > > > > struct perf_counter_context *ctx; > > > > unsigned long flags; > > > > > > > > rcu_read_lock(); > > > > retry: > > > > ctx = rcu_dereference(counter->ctx); > > > > spin_lock_irqsave(&ctx->lock, flags); > > > > if (ctx != rcu_dereference(counter->ctx)) > > > > goto retry; > > > > > > > > *old_gen = ctx->generation; > > > > ctx->generation = ~0ULL; > > > > spin_unlock_irqrestore(&ctx->lock, flags); > > > > rcu_read_unlock(); > > > > > > > > return ctx; > > > > } > > > > > > > > static void unpin_ctx(struct perf_counter_ctx *ctx, u64 old_gen) > > > > { > > > > unsigned long flags; > > > > > > > > spin_lock_irqsave(&ctx->lock, flags); > > > > ctx->generation = old_gen; > > > > spin_unlock_irqrestore(&ctx->lock, flags); > > > > } > > > > > > OK, I think I got this wrong, counter->ctx isn't the problem. > > > task->perf_counter_ctx is. > > > > > > Still would be nice to write it in the above form. I'll go over the code > > > again to see who else might want it. > > > > OK, I went over the code, and your patch does indeed cover the few > > spots we need. It was just my brain going haywire and auditing the > > wrong pattern. > > ok - i'll try this with my 'perf stat make -j' workload that > quickly locks up on a Nehalem. (bug introduced by the context > switch optimizations) nope, that still hangs the box. try the latest Git repo (i tried 95110d7) and do this: make clean perf stat -- make -j that locks up for me, very quickly, with permanently stuck tasks: PID USER PR NI VIRT RES SHR S %CPU %MEM TIME COMMAND 10748 mingo 20 0 0 0 0 R 100.4 0.0 0:06.44 chmod 10756 mingo 20 0 0 0 0 R 100.4 0.0 0:06.43 touch looping in the remove-context retry loop. Ingo