From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752825AbZDGJHd (ORCPT ); Tue, 7 Apr 2009 05:07:33 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751653AbZDGJHX (ORCPT ); Tue, 7 Apr 2009 05:07:23 -0400 Received: from hera.kernel.org ([140.211.167.34]:46936 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751636AbZDGJHW (ORCPT ); Tue, 7 Apr 2009 05:07:22 -0400 Date: Tue, 7 Apr 2009 09:06:48 GMT From: Peter Zijlstra To: linux-tip-commits@vger.kernel.org Cc: linux-kernel@vger.kernel.org, paulus@samba.org, hpa@zytor.com, mingo@redhat.com, a.p.zijlstra@chello.nl, tglx@linutronix.de, cjashfor@linux.vnet.ibm.com, mingo@elte.hu Reply-To: mingo@redhat.com, hpa@zytor.com, paulus@samba.org, linux-kernel@vger.kernel.org, a.p.zijlstra@chello.nl, tglx@linutronix.de, cjashfor@linux.vnet.ibm.com, mingo@elte.hu In-Reply-To: <20090406094517.368446033@chello.nl> References: <20090406094517.368446033@chello.nl> Subject: [tip:perfcounters/core] perf_counter: update mmap() counter read, take 2 Message-ID: Git-Commit-ID: a2e87d06ddbe6e6fdb8d6d2e5e985efe4efb07dd X-Mailer: tip-git-log-daemon MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.0 (hera.kernel.org [127.0.0.1]); Tue, 07 Apr 2009 09:06:50 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: a2e87d06ddbe6e6fdb8d6d2e5e985efe4efb07dd Gitweb: http://git.kernel.org/tip/a2e87d06ddbe6e6fdb8d6d2e5e985efe4efb07dd Author: Peter Zijlstra AuthorDate: Mon, 6 Apr 2009 11:44:59 +0200 Committer: Ingo Molnar CommitDate: Tue, 7 Apr 2009 10:48:54 +0200 perf_counter: update mmap() counter read, take 2 Update the userspace read method. Paul noted that: - userspace cannot observe ->lock & 1 on the same cpu. - we need a barrier() between reading ->lock and ->index to ensure we read them in that prticular order. Signed-off-by: Peter Zijlstra Cc: Paul Mackerras Cc: Corey Ashford LKML-Reference: <20090406094517.368446033@chello.nl> Signed-off-by: Ingo Molnar --- include/linux/perf_counter.h | 24 ++++++++++-------------- 1 files changed, 10 insertions(+), 14 deletions(-) diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h index f2b914d..e22ab47 100644 --- a/include/linux/perf_counter.h +++ b/include/linux/perf_counter.h @@ -170,22 +170,18 @@ struct perf_counter_mmap_page { * u32 seq; * s64 count; * - * again: - * seq = pc->lock; - * if (unlikely(seq & 1)) { - * cpu_relax(); - * goto again; - * } + * do { + * seq = pc->lock; * - * if (pc->index) { - * count = pmc_read(pc->index - 1); - * count += pc->offset; - * } else - * goto regular_read; + * barrier() + * if (pc->index) { + * count = pmc_read(pc->index - 1); + * count += pc->offset; + * } else + * goto regular_read; * - * barrier(); - * if (pc->lock != seq) - * goto again; + * barrier(); + * } while (pc->lock != seq); * * NOTE: for obvious reason this only works on self-monitoring * processes.