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=-19.2 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,URIBL_BLOCKED,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 1863EC433E0 for ; Tue, 12 Jan 2021 00:46:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CF0FF224F9 for ; Tue, 12 Jan 2021 00:46:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731340AbhALAqP (ORCPT ); Mon, 11 Jan 2021 19:46:15 -0500 Received: from mail.kernel.org ([198.145.29.99]:46716 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731185AbhALAqG (ORCPT ); Mon, 11 Jan 2021 19:46:06 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 2658D22D58; Tue, 12 Jan 2021 00:45:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1610412325; bh=Ej3KobiPn6dWwcJWHEBW6abyBS5WpnvKcoB02tTT7hw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=iWmolbOY3u3gVsXodViLZlHFaY5Lch9+A5qv05N1yveyAl3SXuaqMgThzceB+UeEB P9J/sSRizMBagCXdAtpxtDLHqnlhb/uPUty9C1eUnhNytC94C7o9+3iMX8M3yNBs4u 8bkjmJ6QZ7JqnRJwI/RsbUrIxKU4X8pabS3mwI26A4erR6s6sB0KkFyRLSZyACgKBN KmKI48R7ukay8nzlzcX6uAsQAiD+DM8EF0gYboV2qjkP1JM3nIQb+DHXIa7nQJRNg6 aUMo9LCIM+RZVBtEUgBToZv+kEpl8Hq/2XMAcI0orDUVq17EMyuFPjsCVKPJ8AEmom tQHLO1hb2u0iQ== From: paulmck@kernel.org To: linux-kernel@vger.kernel.org Cc: john.stultz@linaro.org, tglx@linutronix.de, sboyd@kernel.org, corbet@lwn.net, Mark.Rutland@arm.com, maz@kernel.org, kernel-team@fb.com, "Paul E. McKenney" Subject: [PATCH v2 clocksource 3/5] clocksource: Check per-CPU clock synchronization when marked unstable Date: Mon, 11 Jan 2021 16:45:18 -0800 Message-Id: <20210112004520.24027-3-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20210112004258.GA23158@paulmck-ThinkPad-P72> References: <20210112004258.GA23158@paulmck-ThinkPad-P72> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" Some sorts of per-CPU clock sources have a history of going out of synchronization with each other. However, this problem has purportedy been solved in the past ten years. Except that it is all too possible that the problem has instead simply been made less likely, which might mean that some of the occasional "Marking clocksource 'tsc' as unstable" messages might be due to desynchronization. How would anyone know? This commit therefore adds CPU-to-CPU synchronization checking for newly unstable clocksource that are marked with the new CLOCK_SOURCE_VERIFY_PERCPU flag. Lists of desynchronized CPUs are printed, with the caveat that if it is the reporting CPU that is itself desynchronized, it will appear that all the other clocks are wrong. Just like in real life. Cc: John Stultz Cc: Thomas Gleixner Cc: Stephen Boyd Cc: Jonathan Corbet Cc: Mark Rutland Cc: Marc Zyngier Reported-by: Chris Mason [ paulmck: Add "static" to clocksource_verify_one_cpu() per kernel test robot feedback. ] Signed-off-by: Paul E. McKenney --- arch/x86/kernel/kvmclock.c | 2 +- arch/x86/kernel/tsc.c | 3 +- include/linux/clocksource.h | 2 +- kernel/time/clocksource.c | 73 +++++++++++++++++++++++++++++++++++++++++++++ 4 files changed, 77 insertions(+), 3 deletions(-) diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c index aa59374..337bb2c 100644 --- a/arch/x86/kernel/kvmclock.c +++ b/arch/x86/kernel/kvmclock.c @@ -169,7 +169,7 @@ struct clocksource kvm_clock = { .read = kvm_clock_get_cycles, .rating = 400, .mask = CLOCKSOURCE_MASK(64), - .flags = CLOCK_SOURCE_IS_CONTINUOUS, + .flags = CLOCK_SOURCE_IS_CONTINUOUS | CLOCK_SOURCE_VERIFY_PERCPU, .enable = kvm_cs_enable, }; EXPORT_SYMBOL_GPL(kvm_clock); diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index f70dffc..5628917 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -1151,7 +1151,8 @@ static struct clocksource clocksource_tsc = { .mask = CLOCKSOURCE_MASK(64), .flags = CLOCK_SOURCE_IS_CONTINUOUS | CLOCK_SOURCE_VALID_FOR_HRES | - CLOCK_SOURCE_MUST_VERIFY, + CLOCK_SOURCE_MUST_VERIFY | + CLOCK_SOURCE_VERIFY_PERCPU, .vdso_clock_mode = VDSO_CLOCKMODE_TSC, .enable = tsc_cs_enable, .resume = tsc_resume, diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h index 86d143d..83a3ebf 100644 --- a/include/linux/clocksource.h +++ b/include/linux/clocksource.h @@ -131,7 +131,7 @@ struct clocksource { #define CLOCK_SOURCE_UNSTABLE 0x40 #define CLOCK_SOURCE_SUSPEND_NONSTOP 0x80 #define CLOCK_SOURCE_RESELECT 0x100 - +#define CLOCK_SOURCE_VERIFY_PERCPU 0x200 /* simplify initialization of mask field */ #define CLOCKSOURCE_MASK(bits) GENMASK_ULL((bits) - 1, 0) diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c index 4663b86..23bcefe 100644 --- a/kernel/time/clocksource.c +++ b/kernel/time/clocksource.c @@ -211,6 +211,78 @@ static void clocksource_watchdog_inject_delay(void) WARN_ON_ONCE(injectfail < 0); } +static struct clocksource *clocksource_verify_work_cs; +static DEFINE_PER_CPU(u64, csnow_mid); +static cpumask_t cpus_ahead; +static cpumask_t cpus_behind; + +static void clocksource_verify_one_cpu(void *csin) +{ + struct clocksource *cs = (struct clocksource *)csin; + + __this_cpu_write(csnow_mid, cs->read(cs)); +} + +static void clocksource_verify_percpu_wq(struct work_struct *unused) +{ + int cpu; + struct clocksource *cs; + int64_t cs_nsec; + u64 csnow_begin; + u64 csnow_end; + u64 delta; + + cs = smp_load_acquire(&clocksource_verify_work_cs); // pairs with release + if (WARN_ON_ONCE(!cs)) + return; + pr_warn("Checking clocksource %s synchronization from CPU %d.\n", + cs->name, smp_processor_id()); + cpumask_clear(&cpus_ahead); + cpumask_clear(&cpus_behind); + csnow_begin = cs->read(cs); + smp_call_function(clocksource_verify_one_cpu, cs, 1); + csnow_end = cs->read(cs); + for_each_online_cpu(cpu) { + if (cpu == smp_processor_id()) + continue; + delta = (per_cpu(csnow_mid, cpu) - csnow_begin) & cs->mask; + if ((s64)delta < 0) + cpumask_set_cpu(cpu, &cpus_behind); + delta = (csnow_end - per_cpu(csnow_mid, cpu)) & cs->mask; + if ((s64)delta < 0) + cpumask_set_cpu(cpu, &cpus_ahead); + } + if (!cpumask_empty(&cpus_ahead)) + pr_warn(" CPUs %*pbl ahead of CPU %d for clocksource %s.\n", + cpumask_pr_args(&cpus_ahead), + smp_processor_id(), cs->name); + if (!cpumask_empty(&cpus_behind)) + pr_warn(" CPUs %*pbl behind CPU %d for clocksource %s.\n", + cpumask_pr_args(&cpus_behind), + smp_processor_id(), cs->name); + if (!cpumask_empty(&cpus_ahead) || !cpumask_empty(&cpus_behind)) { + delta = clocksource_delta(csnow_end, csnow_begin, cs->mask); + cs_nsec = clocksource_cyc2ns(delta, cs->mult, cs->shift); + pr_warn(" CPU %d duration %lldns for clocksource %s.\n", + smp_processor_id(), cs_nsec, cs->name); + } + smp_store_release(&clocksource_verify_work_cs, NULL); // pairs with acquire. +} + +static DECLARE_WORK(clocksource_verify_work, clocksource_verify_percpu_wq); + +static void clocksource_verify_percpu(struct clocksource *cs) +{ + if (!(cs->flags & CLOCK_SOURCE_VERIFY_PERCPU)) + return; + if (smp_load_acquire(&clocksource_verify_work_cs)) { // pairs with release. + pr_warn("Previous clocksource synchronization still in flight.\n"); + return; + } + smp_store_release(&clocksource_verify_work_cs, cs); //pairs with acquire. + queue_work(system_highpri_wq, &clocksource_verify_work); +} + static void clocksource_watchdog(struct timer_list *unused) { struct clocksource *cs; @@ -284,6 +356,7 @@ 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); + clocksource_verify_percpu(cs); __clocksource_unstable(cs); continue; } -- 2.9.5