From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933307Ab0BYSdz (ORCPT ); Thu, 25 Feb 2010 13:33:55 -0500 Received: from relay3.sgi.com ([192.48.152.1]:46498 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S933250Ab0BYSdy (ORCPT ); Thu, 25 Feb 2010 13:33:54 -0500 Date: Thu, 25 Feb 2010 12:33:53 -0600 From: Dimitri Sivanich To: linux-kernel@vger.kernel.org Cc: Pallipadi@sgi.com, Venkatesh , Thomas Gleixner , Ingo Molnar Subject: [PATCH] Fix sched_clock_cpu for systems with unsynchronized TSC Message-ID: <20100225183353.GA21187@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. This patch changes the logic to assume that the sched_clock is stable at first. From then on it is only cleared. Signed-off-by: Dimitri Sivanich --- arch/x86/kernel/cpu/intel.c | 4 ++-- kernel/sched_clock.c | 2 +- 2 files changed, 3 insertions(+), 3 deletions(-) Index: linux/arch/x86/kernel/cpu/intel.c =================================================================== --- linux.orig/arch/x86/kernel/cpu/intel.c +++ linux/arch/x86/kernel/cpu/intel.c @@ -70,8 +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; - } + } else + sched_clock_stable = 0; /* * There is a known erratum on Pentium III and Core Solo Index: linux/kernel/sched_clock.c =================================================================== --- linux.orig/kernel/sched_clock.c +++ linux/kernel/sched_clock.c @@ -45,7 +45,7 @@ unsigned long long __attribute__((weak)) static __read_mostly int sched_clock_running; #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK -__read_mostly int sched_clock_stable; +__read_mostly int sched_clock_stable = 1; struct sched_clock_data { u64 tick_raw;