Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932535AbcDBAzz (ORCPT ); Fri, 1 Apr 2016 20:55:55 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:54145 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932374AbcDBAzv (ORCPT ); Fri, 1 Apr 2016 20:55:51 -0400 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Thomas Gleixner , Frederic Weisbecker , Glauber Costa , Linus Torvalds , Peter Zijlstra , Ingo Molnar , Kamal Mostafa Subject: [PATCH 3.19.y-ckt 065/170] sched/cputime: Fix steal time accounting vs. CPU hotplug Date: Fri, 1 Apr 2016 17:52:31 -0700 Message-Id: <1459558456-24452-66-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1459558456-24452-1-git-send-email-kamal@canonical.com> References: <1459558456-24452-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 3.19 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3066 Lines: 85 3.19.8-ckt18 -stable review patch. If anyone has any objections, please let me know. ---8<------------------------------------------------------------ From: Thomas Gleixner commit e9532e69b8d1d1284e8ecf8d2586de34aec61244 upstream. On CPU hotplug the steal time accounting can keep a stale rq->prev_steal_time value over CPU down and up. So after the CPU comes up again the delta calculation in steal_account_process_tick() wreckages itself due to the unsigned math: u64 steal = paravirt_steal_clock(smp_processor_id()); steal -= this_rq()->prev_steal_time; So if steal is smaller than rq->prev_steal_time we end up with an insane large value which then gets added to rq->prev_steal_time, resulting in a permanent wreckage of the accounting. As a consequence the per CPU stats in /proc/stat become stale. Nice trick to tell the world how idle the system is (100%) while the CPU is 100% busy running tasks. Though we prefer realistic numbers. None of the accounting values which use a previous value to account for fractions is reset at CPU hotplug time. update_rq_clock_task() has a sanity check for prev_irq_time and prev_steal_time_rq, but that sanity check solely deals with clock warps and limits the /proc/stat visible wreckage. The prev_time values are still wrong. Solution is simple: Reset rq->prev_*_time when the CPU is plugged in again. Signed-off-by: Thomas Gleixner Acked-by: Rik van Riel Cc: Frederic Weisbecker Cc: Glauber Costa Cc: Linus Torvalds Cc: Peter Zijlstra Fixes: commit 095c0aa83e52 "sched: adjust scheduler cpu power for stolen time" Fixes: commit aa483808516c "sched: Remove irq time from available CPU power" Fixes: commit e6e6685accfa "KVM guest: Steal time accounting" Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1603041539490.3686@nanos Signed-off-by: Ingo Molnar Signed-off-by: Kamal Mostafa --- kernel/sched/core.c | 1 + kernel/sched/sched.h | 13 +++++++++++++ 2 files changed, 14 insertions(+) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 6b5909b..e5963b3 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5314,6 +5314,7 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu) case CPU_UP_PREPARE: rq->calc_load_update = calc_load_update; + account_reset_rq(rq); break; case CPU_ONLINE: diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 6183e4b..0efd0fe 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1613,3 +1613,16 @@ static inline u64 irq_time_read(int cpu) } #endif /* CONFIG_64BIT */ #endif /* CONFIG_IRQ_TIME_ACCOUNTING */ + +static inline void account_reset_rq(struct rq *rq) +{ +#ifdef CONFIG_IRQ_TIME_ACCOUNTING + rq->prev_irq_time = 0; +#endif +#ifdef CONFIG_PARAVIRT + rq->prev_steal_time = 0; +#endif +#ifdef CONFIG_PARAVIRT_TIME_ACCOUNTING + rq->prev_steal_time_rq = 0; +#endif +} -- 2.7.4