Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933229AbcKOUVY (ORCPT ); Tue, 15 Nov 2016 15:21:24 -0500 Received: from mga14.intel.com ([192.55.52.115]:61335 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752415AbcKOUVO (ORCPT ); Tue, 15 Nov 2016 15:21:14 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.31,496,1473145200"; d="scan'208";a="786813644" From: Bin Gao To: Thomas Gleixner Cc: Ingo Molnar , H Peter Anvin , x86@kernel.org, Peter Zijlstra , linux-kernel@vger.kernel.org, Bin Gao Subject: [PATCH 1/4] x86/tsc: add X86_FEATURE_TSC_KNOWN_FREQ flag Date: Tue, 15 Nov 2016 12:27:21 -0800 Message-Id: <1479241644-234277-2-git-send-email-bin.gao@linux.intel.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1479241644-234277-1-git-send-email-bin.gao@linux.intel.com> References: <1479241644-234277-1-git-send-email-bin.gao@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2678 Lines: 59 The X86_FEATURE_TSC_RELIABLE flag in Linux kernel implies both reliable (at runtime) and trustable (at calibration). But reliable running and trustable calibration are logically irrelevant. Per Thomas Gleixner's suggestion we would like to split this flag into two separate flags: X86_FEATURE_TSC_RELIABLE - running reliably X86_FEATURE_TSC_KNOWN_FREQ - frequency is known (no calibration required) These two flags allow Linux kernel to act differently based on processor/SoC's capability, i.e. no watchdog on TSC if TSC is reliable, and no calibration if TSC frequency is known. Current Linux kernel already gurantees calibration is skipped for processors that can report TSC frequency by CPUID or MSR. However, the delayed calibration is still not skipped for these CPUID/MSR capable processors. The new flag X86_FEATURE_TSC_KNOWN_FREQ added by this patch will gurantee the delayed calibration is skipped. Signed-off-by: Bin Gao --- arch/x86/include/asm/cpufeatures.h | 1 + arch/x86/kernel/tsc.c | 11 ++++++++--- 2 files changed, 9 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h index a396292..7f6a5f8 100644 --- a/arch/x86/include/asm/cpufeatures.h +++ b/arch/x86/include/asm/cpufeatures.h @@ -106,6 +106,7 @@ #define X86_FEATURE_APERFMPERF ( 3*32+28) /* APERFMPERF */ #define X86_FEATURE_EAGER_FPU ( 3*32+29) /* "eagerfpu" Non lazy FPU restore */ #define X86_FEATURE_NONSTOP_TSC_S3 ( 3*32+30) /* TSC doesn't stop in S3 state */ +#define X86_FEATURE_TSC_KNOWN_FREQ ( 3*32+31) /* TSC has known frequency */ /* Intel-defined CPU features, CPUID level 0x00000001 (ecx), word 4 */ #define X86_FEATURE_XMM3 ( 4*32+ 0) /* "pni" SSE-3 */ diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 46b2f41..3ba146e 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -1283,10 +1283,15 @@ static int __init init_tsc_clocksource(void) clocksource_tsc.flags |= CLOCK_SOURCE_SUSPEND_NONSTOP; /* - * Trust the results of the earlier calibration on systems - * exporting a reliable TSC. + * When TSC frequency is known (generally got by MSR or CPUID), we skip + * the refined calibration and directly register it as a clocksource. + * + * We still keep the TSC_RELIABLE flag here to avoid regression - + * it will be removed after all the conversion for other code paths + * connected to this flag is done. */ - if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE)) { + if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE) || + boot_cpu_has(X86_FEATURE_TSC_KNOWN_FREQ)) { clocksource_register_khz(&clocksource_tsc, tsc_khz); return 0; } -- 1.9.1