From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756126Ab2BGMJD (ORCPT ); Tue, 7 Feb 2012 07:09:03 -0500 Received: from mail.skyhub.de ([78.46.96.112]:47686 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754009Ab2BGMJA (ORCPT ); Tue, 7 Feb 2012 07:09:00 -0500 From: Borislav Petkov To: Ingo Molnar Cc: Borislav Petkov , Venki Pallipadi , Peter Zijlstra , Stephane Eranian , LKML , Arnaldo Carvalho de Melo , Robert Richter , Eric Dumazet , Andreas Herrmann , Borislav Petkov Subject: [PATCH] x86, AMD: Set sched_clock_stable Date: Tue, 7 Feb 2012 13:08:52 +0100 Message-Id: <1328616532-13783-1-git-send-email-bp@alien8.de> X-Mailer: git-send-email 1.7.9 In-Reply-To: <20120207095000.GF15359@elte.hu> References: <20120207095000.GF15359@elte.hu> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Stephane Eranian reported that doing a scheduler latency measurements with perf on AMD doesn't work out as expected due to the fact that the sched_clock() granularity is too coarse, i.e. done in jiffies due to the sched_clock_stable not set, which, if set, would mean that we get to use the TSC as sample source which would give us much higher precision. However, there's no reason not to set sched_clock_stable on AMD because all families from F10h and upwards do have an invariant TSC and have the CPUID flag to prove (CPUID_8000_0007_EDX[8]). Make it so, #1. Signed-off-by: Borislav Petkov Cc: Stephane Eranian Cc: Peter Zijlstra Cc: Ingo Molnar Link: http://lkml.kernel.org/r/20120206132546.GA30854@quad --- arch/x86/kernel/cpu/amd.c | 3 +++ 1 files changed, 3 insertions(+), 0 deletions(-) diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c index f4773f4..0a44b90 100644 --- a/arch/x86/kernel/cpu/amd.c +++ b/arch/x86/kernel/cpu/amd.c @@ -5,6 +5,7 @@ #include #include +#include #include #include #include @@ -456,6 +457,8 @@ static void __cpuinit early_init_amd(struct cpuinfo_x86 *c) if (c->x86_power & (1 << 8)) { set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC); set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC); + if (!check_tsc_unstable()) + sched_clock_stable = 1; } #ifdef CONFIG_X86_64 -- 1.7.9