From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754502AbZF0K5T (ORCPT ); Sat, 27 Jun 2009 06:57:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752116AbZF0K5K (ORCPT ); Sat, 27 Jun 2009 06:57:10 -0400 Received: from relay2.sgi.com ([192.48.179.30]:48153 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751919AbZF0K5J (ORCPT ); Sat, 27 Jun 2009 06:57:09 -0400 Date: Sat, 27 Jun 2009 05:57:11 -0500 From: Robin Holt To: linux-kernel@vger.kernel.org Subject: [Patch] stop_machine stalls for a considerable period on large cpu count machines. Message-ID: <20090627105711.GB6894@sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I forgot to include the linux-kernel mailing list. Robin ----- Forwarded message from Robin Holt ----- Date: Sat, 27 Jun 2009 05:53:11 -0500 From: Robin Holt To: Linus Torvalds Cc: Rusty Russell , stable@kernel.org, mike travis Subject: [Patch] stop_machine stalls for a considerable period on large cpu count machines. Mike Travis noted that a 2048 cpu machine booting would take hours to get through its modprobes. We would get numerous back traces from stop_cpu indicating they had not serviced interrupts. A quick code review indicated we have a situation of heavy cacheline contention due to the 'state' (read-mostly) and 'thread_ack' (write-mostly) variables being located in the same cacheline. Signed-off-by: Robin Holt --- kernel/stop_machine.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) Index: stop_machine_false_sharing/kernel/stop_machine.c =================================================================== --- stop_machine_false_sharing.orig/kernel/stop_machine.c 2009-06-27 05:26:57.000000000 -0500 +++ stop_machine_false_sharing/kernel/stop_machine.c 2009-06-27 05:34:45.182637682 -0500 @@ -36,8 +36,8 @@ struct stop_machine_data { /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */ static unsigned int num_threads; -static atomic_t thread_ack; -static DEFINE_MUTEX(lock); +static atomic_t thread_ack ____cacheline_aligned; +static DEFINE_MUTEX(lock) ____cacheline_aligned; /* setup_lock protects refcount, stop_machine_wq and stop_machine_work. */ static DEFINE_MUTEX(setup_lock); /* Users of stop_machine. */ ----- End forwarded message -----