From nobody Sun Feb 8 01:51:57 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 75F39C77B75 for ; Mon, 22 May 2023 03:37:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229947AbjEVDhT (ORCPT ); Sun, 21 May 2023 23:37:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56370 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229501AbjEVDhC (ORCPT ); Sun, 21 May 2023 23:37:02 -0400 Received: from mga11.intel.com (mga11.intel.com [192.55.52.93]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EBB7DA2 for ; Sun, 21 May 2023 20:37:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1684726621; x=1716262621; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=P59aXtyfm/ISccYK7l1gh94sKmTWDcB1nL/Li5f4TEA=; b=k5R3ktOXkdkt0+QT6+0OUnnjFlCtu1g5BcSiKlgOnMr8fWofsbXdACSw 2JM03bymWJiWZ/FDw9y9IKYZmafvavn0fkU7gt+bDOEjE1WfFRCxCXVCA QayN3eETImf5BnjwyPN4Nf8EWQEsQazCW2NJ/lgaX2AbeYys3O85MHbps Hy4Gw7MAVhHh4NT1axLbn+TSYreprOi10XyxozdEi33VNt8a9TdN7jjpm 7nkqtTxkMVk2U+yxFIzjRoYzo/zhcPAeS7Gv3g7bew+sByTY6eMe/4Pn2 LnET4VN1atNRHmo70FimFJx8UWrcm0avaeSHLsmcsMNtg3EJHjyDoCG3q g==; X-IronPort-AV: E=McAfee;i="6600,9927,10717"; a="350327417" X-IronPort-AV: E=Sophos;i="6.00,183,1681196400"; d="scan'208";a="350327417" Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 May 2023 20:37:01 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10717"; a="815499748" X-IronPort-AV: E=Sophos;i="6.00,183,1681196400"; d="scan'208";a="815499748" Received: from feng-clx.sh.intel.com ([10.238.200.228]) by fmsmga002.fm.intel.com with ESMTP; 21 May 2023 20:36:59 -0700 From: Feng Tang To: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H . Peter Anvin" , Peter Zijlstra , paulmck@kernel.org, rui.zhang@intel.com, x86@kernel.org, linux-kernel@vger.kernel.org Cc: Feng Tang Subject: [PATCH RFC] x86/tsc: Make recalibration default on for TSC_KNOWN_FREQ cases Date: Mon, 22 May 2023 11:30:18 +0800 Message-Id: <20230522033018.1276836-1-feng.tang@intel.com> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Commit a7ec817d5542 ("x86/tsc: Add option to force frequency recalibration with HW timer") was added to handle cases that the firmware has bug and provides a wrong TSC frequency number, and it is optional given that this kind of firmware issue rarely happens (Paul reported once [1]). But Rui reported that some Sapphire Rapids platform met this issue again recently, and as firmware is also a kind of 'software' which can't be bug free, make the recalibration default on. When the values from firmware and HW timer's calibration have big gap, raise a warning and let vendor to check which side is broken. One downside is, many VMs also has X86_FEATURE_TSC_KNOWN_FREQ set, and they will also do this recalibration. [1]. https://lore.kernel.org/lkml/20221117230910.GI4001@paulmck-ThinkPad-P1= 7-Gen-1/ Signed-off-by: Feng Tang --- Documentation/admin-guide/kernel-parameters.txt | 4 ---- arch/x86/kernel/tsc.c | 14 ++++---------- 2 files changed, 4 insertions(+), 14 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentatio= n/admin-guide/kernel-parameters.txt index 9e5bab29685f..a826ab3b5dfb 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -6451,10 +6451,6 @@ in situations with strict latency requirements (where interruptions from clocksource watchdog are not acceptable). - [x86] recalibrate: force recalibration against a HW timer - (HPET or PM timer) on systems whose TSC frequency was - obtained from HW or FW using either an MSR or CPUID(0x15). - Warn if the difference is more than 500 ppm. [x86] watchdog: Use TSC as the watchdog clocksource with which to check other HW timers (HPET or PM timer), but only on systems where TSC has been deemed trustworthy. diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 344698852146..b77c5b1ad304 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -48,8 +48,6 @@ static DEFINE_STATIC_KEY_FALSE(__use_tsc); =20 int tsc_clocksource_reliable; =20 -static int __read_mostly tsc_force_recalibrate; - static u32 art_to_tsc_numerator; static u32 art_to_tsc_denominator; static u64 art_to_tsc_offset; @@ -310,8 +308,6 @@ static int __init tsc_setup(char *str) __func__); tsc_as_watchdog =3D 0; } - if (!strcmp(str, "recalibrate")) - tsc_force_recalibrate =3D 1; if (!strcmp(str, "watchdog")) { if (no_tsc_watchdog) pr_alert("%s: tsc=3Dwatchdog overridden by earlier tsc=3Dnowatchdog\n", @@ -1395,7 +1391,6 @@ static void tsc_refine_calibration_work(struct work_s= truct *work) else freq =3D calc_pmtimer_ref(delta, ref_start, ref_stop); =20 - /* Will hit this only if tsc_force_recalibrate has been set */ if (boot_cpu_has(X86_FEATURE_TSC_KNOWN_FREQ)) { =20 /* Warn if the deviation exceeds 500 ppm */ @@ -1456,17 +1451,16 @@ static int __init init_tsc_clocksource(void) clocksource_tsc.flags |=3D CLOCK_SOURCE_SUSPEND_NONSTOP; =20 /* - * When TSC frequency is known (retrieved via MSR or CPUID), we skip - * the refined calibration and directly register it as a clocksource. + * When TSC frequency is known (retrieved via MSR or CPUID), we + * directly register it as a clocksource. As the firmware could + * be wrong (very unlikely) about the values, the recalibration + * by hardware timer is kept just as a sanity check. */ if (boot_cpu_has(X86_FEATURE_TSC_KNOWN_FREQ)) { if (boot_cpu_has(X86_FEATURE_ART)) art_related_clocksource =3D &clocksource_tsc; clocksource_register_khz(&clocksource_tsc, tsc_khz); clocksource_unregister(&clocksource_tsc_early); - - if (!tsc_force_recalibrate) - return 0; } =20 schedule_delayed_work(&tsc_irqwork, 0); --=20 2.34.1