From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1423041AbXBBAgD (ORCPT ); Thu, 1 Feb 2007 19:36:03 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1423040AbXBBAgB (ORCPT ); Thu, 1 Feb 2007 19:36:01 -0500 Received: from e32.co.us.ibm.com ([32.97.110.150]:35371 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1423035AbXBBAf6 (ORCPT ); Thu, 1 Feb 2007 19:35:58 -0500 Date: Thu, 1 Feb 2007 16:35:50 -0800 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Subject: Fw: [patch] posix timers: RCU optimization for clock_gettime() Message-ID: <20070202003550.GA17012@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org The attached patch uses RCU to avoid the need to acquire tasklist_lock in the single-threaded case of clock_gettime(). It still acquires tasklist_lock when for a (potentially multithreaded) process. This change allows realtime applications to frequently monitor CPU consumption of individual tasks, as requested (and now deployed) by some off-list users. This has been in Ingo Molnar's -rt patchset since late 2005 with no problems reported, and tests successfully on 2.6.20-rc6, so I believe that it is long-since ready for mainline adoption. Signed-off-by: Paul E. McKenney Signed-off-by: Ingo Molnar --- kernel/posix-cpu-timers.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) Index: linux/kernel/posix-cpu-timers.c =================================================================== --- linux.orig/kernel/posix-cpu-timers.c +++ linux/kernel/posix-cpu-timers.c @@ -304,7 +304,7 @@ int posix_cpu_clock_get(const clockid_t * should be able to see it. */ struct task_struct *p; - read_lock(&tasklist_lock); + rcu_read_lock(); p = find_task_by_pid(pid); if (p) { if (CPUCLOCK_PERTHREAD(which_clock)) { @@ -313,11 +313,13 @@ int posix_cpu_clock_get(const clockid_t p, &rtn); } } else if (p->tgid == pid && p->signal) { + read_lock(&tasklist_lock); error = cpu_clock_sample_group(which_clock, p, &rtn); + read_unlock(&tasklist_lock); } } - read_unlock(&tasklist_lock); + rcu_read_unlock(); } if (error) ----- End forwarded message -----