Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754015AbZAFQ1y (ORCPT ); Tue, 6 Jan 2009 11:27:54 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751229AbZAFQ1o (ORCPT ); Tue, 6 Jan 2009 11:27:44 -0500 Received: from relay3.sgi.com ([192.48.171.31]:48082 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750846AbZAFQ1n (ORCPT ); Tue, 6 Jan 2009 11:27:43 -0500 Date: Tue, 6 Jan 2009 10:27:41 -0600 From: Dimitri Sivanich To: linux-ia64@vger.kernel.org, Tony Luck , Greg KH Cc: linux-kernel@vger.kernel.org, Peter Zijlstra , Gregory Haskins , Nick Piggin , Tony Luck , Robin Holt Subject: [PATCH] configure HAVE_UNSTABLE_SCHED_CLOCK for SGI_SN systems Message-ID: <20090106162741.GA7991@sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1515 Lines: 42 Turn on CONFIG_HAVE_UNSTABLE_SCHED_CLOCK for SGI_SN. SGI Altix has unsynchronized itc clocks. This results in rq->clock occasionally being set to a time in the past by a remote cpu. Note that it is possible that this problem may exist for other ia64 machines as well, based on the following comment for sched_clock() in arch/ia64/kernel/head.S: * Return a CPU-local timestamp in nano-seconds. This timestamp is * NOT synchronized across CPUs its return value must never be * compared against the values returned on another CPU. The usage in * kernel/sched.c ensures that. Signed-off-by: Dimitri Sivanich --- Greg, if everyone is OK with this patch, this should also be applied to all stable trees starting with 2.6.26. arch/ia64/Kconfig | 1 + 1 file changed, 1 insertion(+) Index: linux-2.6/arch/ia64/Kconfig =================================================================== --- linux-2.6.orig/arch/ia64/Kconfig 2009-01-06 10:13:13.051918923 -0600 +++ linux-2.6/arch/ia64/Kconfig 2009-01-06 10:13:44.547856328 -0600 @@ -536,6 +536,7 @@ config IA64_MC_ERR_INJECT config SGI_SN def_bool y if (IA64_SGI_SN2 || IA64_GENERIC) + select HAVE_UNSTABLE_SCHED_CLOCK config IA64_ESI bool "ESI (Extensible SAL Interface) support" -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/