From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751496Ab0CARsS (ORCPT ); Mon, 1 Mar 2010 12:48:18 -0500 Received: from relay3.sgi.com ([192.48.152.1]:37285 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750976Ab0CARsR (ORCPT ); Mon, 1 Mar 2010 12:48:17 -0500 Date: Mon, 1 Mar 2010 11:48:15 -0600 From: Dimitri Sivanich To: linux-kernel@vger.kernel.org Cc: "H. Peter Anvin" , venkatesh.pallipadi@intel.com, Thomas Gleixner , Ingo Molnar Subject: [PATCH v2] x86: Fix sched_clock_cpu for systems with unsynchronized TSC Message-ID: <20100301174815.GC8224@sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- Only affects x86 arch. arch/x86/kernel/cpu/intel.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) Index: linux/arch/x86/kernel/cpu/intel.c =================================================================== --- linux.orig/arch/x86/kernel/cpu/intel.c +++ linux/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; } /*