From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932763Ab0C3XXU (ORCPT ); Tue, 30 Mar 2010 19:23:20 -0400 Received: from kroah.org ([198.145.64.141]:46841 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754633Ab0C3XWV (ORCPT ); Tue, 30 Mar 2010 19:22:21 -0400 X-Mailbox-Line: From linux@linux.site Tue Mar 30 15:49:00 2010 Message-Id: <20100330224859.521323575@linux.site> User-Agent: quilt/0.47-14.9 Date: Tue, 30 Mar 2010 15:43:07 -0700 From: Greg KH To: linux-kernel@vger.kernel.org, stable@kernel.org Cc: stable-review@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Dimitri Sivanich , Venkatesh Pallipadi , Peter Zijlstra , Ingo Molnar , Greg Kroah-Hartman Subject: [153/156] x86: Fix sched_clock_cpu for systems with unsynchronized TSC In-Reply-To: <20100330230630.GA28824@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Dimitri Sivanich commit 14be1f7454ea96ee614467a49cf018a1a383b189 upstream. On UV systems, the TSC is not synchronized across blades. The sched_clock_cpu() function is returning values that can go backwards (I've seen as much as 8 seconds) when switching between cpus. As each cpu comes up, early_init_intel() will currently set the sched_clock_stable flag true. When mark_tsc_unstable() runs, it clears the flag, but this only occurs once (the first time a cpu comes up whose TSC is not synchronized with cpu 0). After this, early_init_intel() will set the flag again as the next cpu comes up. Only set sched_clock_stable if tsc has not been marked unstable. Signed-off-by: Dimitri Sivanich Acked-by: Venkatesh Pallipadi Acked-by: Peter Zijlstra LKML-Reference: <20100301174815.GC8224@sgi.com> Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/cpu/intel.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/arch/x86/kernel/cpu/intel.c +++ b/arch/x86/kernel/cpu/intel.c @@ -70,7 +70,8 @@ static void __cpuinit early_init_intel(s if (c->x86_power & (1 << 8)) { set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC); set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC); - sched_clock_stable = 1; + if (!check_tsc_unstable()) + sched_clock_stable = 1; } /*