From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-19.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1A2FFC433B4 for ; Wed, 14 Apr 2021 04:36:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F0BF7613B1 for ; Wed, 14 Apr 2021 04:36:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232462AbhDNEgc (ORCPT ); Wed, 14 Apr 2021 00:36:32 -0400 Received: from mail.kernel.org ([198.145.29.99]:42848 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230465AbhDNEgZ (ORCPT ); Wed, 14 Apr 2021 00:36:25 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 7AD68613C1; Wed, 14 Apr 2021 04:36:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1618374964; bh=8g3kzPeNL395r7Fn/+Wokm2rUjHXGOfitjVm0eJPi+w=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=A4MG1euBH2lReg2IbPLve7JqMGPgBbsed8GlG5GUw9u/yynNl5ILnnK51eAEDh7hs oP5CwOeoAdHFjxb6QnR3h8gHRSEzW9d8w0wCvYJARQDce0+K99hhEC6hbrZK8GHwbA 9nTnBm76BBXWRYYIWqocjT+LW6Qs1WFdSYqh5ODKuOsD6d3PEes4hxiHPyLKUNfBCr gtpCOXMV3x73h1xNNdOloTxABbAHHQD36EWcEaG32sWafL3ZXwzn1w+qH1m/l3aELs WYK9Ggy8yLGbmKtK0U1BcNJeOXBHqWMTLERzKS2zpUeat6Le4AUSgFOsVgQ9FcqTLJ fk9x35qUZtvTw== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 3F49B5C26E0; Tue, 13 Apr 2021 21:36:04 -0700 (PDT) From: "Paul E. McKenney" To: tglx@linutronix.de Cc: linux-kernel@vger.kernel.org, john.stultz@linaro.org, sboyd@kernel.org, corbet@lwn.net, Mark.Rutland@arm.com, maz@kernel.org, kernel-team@fb.com, neeraju@codeaurora.org, ak@linux.intel.com, "Paul E. McKenney" Subject: [PATCH v8 clocksource 5/5] clocksource: Limit number of CPUs checked for clock synchronization Date: Tue, 13 Apr 2021 21:36:02 -0700 Message-Id: <20210414043602.2812981-5-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20210414043435.GA2812539@paulmck-ThinkPad-P17-Gen-1> References: <20210414043435.GA2812539@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Currently, if skew is detected on a clock marked CLOCK_SOURCE_VERIFY_PERCPU, that clock is checked on all CPUs. This is thorough, but might not be what you want on a system with a few tens of CPUs, let alone a few hundred of them. Therefore, by default check only up to eight randomly chosen CPUs. Also provide a new clocksource.verify_n_cpus kernel boot parameter. A value of -1 says to check all of the CPUs, and a non-negative value says to randomly select that number of CPUs, without concern about selecting the same CPU multiple times. However, make use of a cpumask so that a given CPU will be checked at most once. Suggested-by: Thomas Gleixner # For verify_n_cpus=1. Cc: John Stultz Cc: Thomas Gleixner Cc: Stephen Boyd Cc: Jonathan Corbet Cc: Mark Rutland Cc: Marc Zyngier Cc: Andi Kleen Signed-off-by: Paul E. McKenney --- .../admin-guide/kernel-parameters.txt | 10 +++ kernel/time/clocksource.c | 74 ++++++++++++++++++- 2 files changed, 82 insertions(+), 2 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index f9da90f2791f..c09be8392bd6 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -621,6 +621,16 @@ unstable. Defaults to three retries, that is, four attempts to read the clock under test. + clocksource.verify_n_cpus= [KNL] + Limit the number of CPUs checked for clocksources + marked with CLOCK_SOURCE_VERIFY_PERCPU that + are marked unstable due to excessive skew. + A negative value says to check all CPUs, while + zero says not to check any. Values larger than + nr_cpu_ids are silently truncated to nr_cpu_ids. + The actual CPUs are chosen randomly, with + no replacement if the same CPU is chosen twice. + clearcpuid=BITNUM[,BITNUM...] [X86] Disable CPUID feature X for the kernel. See arch/x86/include/asm/cpufeatures.h for the valid bit diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index 5f641b15ec6c..8f4967e59b05 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -15,6 +15,8 @@ #include #include #include +#include +#include #include "tick-internal.h" #include "timekeeping_internal.h" @@ -194,6 +196,8 @@ static int inject_delay_shift_percpu = -1; module_param(inject_delay_shift_percpu, int, 0644); static int max_read_retries = 3; module_param(max_read_retries, int, 0644); +static int verify_n_cpus = 8; +module_param(verify_n_cpus, int, 0644); static void clocksource_watchdog_inject_delay(void) { @@ -216,6 +220,55 @@ static void clocksource_watchdog_inject_delay(void) static u64 csnow_mid; static cpumask_t cpus_ahead; static cpumask_t cpus_behind; +static cpumask_t cpus_chosen; + +static void clocksource_verify_choose_cpus(void) +{ + int cpu, i, n = verify_n_cpus; + + if (n < 0) { + /* Check all of the CPUs. */ + cpumask_copy(&cpus_chosen, cpu_online_mask); + cpumask_clear_cpu(smp_processor_id(), &cpus_chosen); + return; + } + + /* If no checking desired, or no other CPU to check, leave. */ + cpumask_clear(&cpus_chosen); + if (n == 0 || num_online_cpus() <= 1) + return; + + /* Make sure to select at least one CPU other than the current CPU. */ + cpu = cpumask_next(-1, cpu_online_mask); + if (cpu == smp_processor_id()) + cpu = cpumask_next(cpu, cpu_online_mask); + if (WARN_ON_ONCE(cpu >= nr_cpu_ids)) + return; + cpumask_set_cpu(cpu, &cpus_chosen); + + /* Force a sane value for the boot parameter. */ + if (n > nr_cpu_ids) + n = nr_cpu_ids - 1; + + /* + * Randomly select the specified number of CPUs. If the same + * CPU is selected multiple times, that CPU is checked only once, + * and no replacement CPU is selected. This gracefully handles + * situations where verify_n_cpus is greater than the number of + * CPUs that are currently online. + */ + for (i = 1; i < n; i++) { + cpu = prandom_u32() % n; + cpu = cpumask_next(cpu - 1, cpu_online_mask); + if (cpu >= nr_cpu_ids) + cpu = cpumask_next(-1, cpu_online_mask); + if (!WARN_ON_ONCE(cpu >= nr_cpu_ids)) + cpumask_set_cpu(cpu, &cpus_chosen); + } + + /* Don't verify ourselves. */ + cpumask_clear_cpu(smp_processor_id(), &cpus_chosen); +} static void clocksource_verify_one_cpu(void *csin) { @@ -239,12 +292,22 @@ static void clocksource_verify_percpu(struct clocksource *cs) s64 delta; int cpu; + if (verify_n_cpus == 0) + return; cpumask_clear(&cpus_ahead); cpumask_clear(&cpus_behind); + get_online_cpus(); preempt_disable(); + clocksource_verify_choose_cpus(); + if (cpumask_weight(&cpus_chosen) == 0) { + preempt_enable(); + put_online_cpus(); + pr_warn("Not enough CPUs to check clocksource '%s'.\n", cs->name); + return; + } testcpu = smp_processor_id(); - pr_warn("Checking clocksource %s synchronization from CPU %d.\n", cs->name, testcpu); - for_each_online_cpu(cpu) { + pr_warn("Checking clocksource %s synchronization from CPU %d to CPUs %*pbl.\n", cs->name, testcpu, cpumask_pr_args(&cpus_chosen)); + for_each_cpu(cpu, &cpus_chosen) { if (cpu == testcpu) continue; csnow_begin = cs->read(cs); @@ -265,6 +328,7 @@ static void clocksource_verify_percpu(struct clocksource *cs) firsttime = 0; } preempt_enable(); + put_online_cpus(); if (!cpumask_empty(&cpus_ahead)) pr_warn(" CPUs %*pbl ahead of CPU %d for clocksource %s.\n", cpumask_pr_args(&cpus_ahead), testcpu, cs->name); @@ -350,6 +414,12 @@ static void clocksource_watchdog(struct timer_list *unused) watchdog->name, wdnow, wdlast, watchdog->mask); pr_warn(" '%s' cs_now: %llx cs_last: %llx mask: %llx\n", cs->name, csnow, cslast, cs->mask); + if (curr_clocksource == cs) + pr_warn(" '%s' is current clocksource.\n", cs->name); + else if (curr_clocksource) + pr_warn(" '%s' (not '%s') is current clocksource.\n", curr_clocksource->name, cs->name); + else + pr_warn(" No current clocksource.\n"); __clocksource_unstable(cs); continue; } -- 2.25.1