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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, 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 2288ECA9EAF for ; Fri, 25 Oct 2019 02:03:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E8AD321D71 for ; Fri, 25 Oct 2019 02:03:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571968993; bh=RU2jcOFbNMVgSwsqFfCLTfXF+sdcXqGu7Jpw7yqMKAA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=FiNatxFE6Fkdj8BCTKBfR+e0BiRbIiQBpgmZlt/HnpTiP/76PDR6zhTm8XISTIUDv lhFj4zlWRV2YTJYuDGnt3Puu5oLtmmoSGfzjz8+hYHSzABOc9TY/pLvluLDtbFBPvT vpjHYy9QeDVj6g6DtQsLTbELzdj5f1aPvvbD6QHI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389704AbfJYCDL (ORCPT ); Thu, 24 Oct 2019 22:03:11 -0400 Received: from mail.kernel.org ([198.145.29.99]:52634 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389657AbfJYCDL (ORCPT ); Thu, 24 Oct 2019 22:03:11 -0400 Received: from lenoir.home (lfbn-ncy-1-150-155.w83-194.abo.wanadoo.fr [83.194.232.155]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0B43321929; Fri, 25 Oct 2019 02:03:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571968989; bh=RU2jcOFbNMVgSwsqFfCLTfXF+sdcXqGu7Jpw7yqMKAA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=me0ybjEJ5+t6wajK6bYAJOI65Y8y2TidBH0CpkMubV57cY9zCfb9xo0NCqAayf7iS wraH0zyT3Jv0C2twNQoxAfmAnjThi/ARkjgcUz4KuyCRl7BVMa+OSpkJreZSUhnxIB MWORDY5tGkfAnFB5fMTlE0iAhkTwctiHdej7ywU0= From: Frederic Weisbecker To: Peter Zijlstra Cc: LKML , Frederic Weisbecker , Wanpeng Li , Rik van Riel , Thomas Gleixner , Yauheni Kaliuta , Ingo Molnar Subject: [PATCH 11/14 v2] sched/kcpustat: Introduce vtime-aware kcpustat accessor for CPUTIME_SYSTEM Date: Fri, 25 Oct 2019 04:03:03 +0200 Message-Id: <20191025020303.19342-1-frederic@kernel.org> X-Mailer: git-send-email 2.23.0 In-Reply-To: <20191016025700.31277-12-frederic@kernel.org> References: <20191016025700.31277-12-frederic@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Kcpustat is not correctly supported on nohz_full CPUs. The tick doesn't fire and the cputime therefore doesn't move forward. The issue has shown up after the vanishing of the remaining 1Hz which has made the stall visible. We are solving that with checking the task running on a CPU through RCU and reading its vtime delta that we add to the raw kcpustat values. We make sure that we fetch a coherent raw-kcpustat/vtime-delta couple sequence while checking that the CPU referred by the target vtime is the correct one, under the locked vtime seqcount. Only CPUTIME_SYSTEM is handled here as a start because it's the trivial case. User and guest time will require more preparation work to correctly handle niceness. Reported-by: Yauheni Kaliuta Signed-off-by: Frederic Weisbecker Cc: Yauheni Kaliuta Cc: Thomas Gleixner Cc: Rik van Riel Cc: Peter Zijlstra Cc: Wanpeng Li Cc: Ingo Molnar --- include/linux/kernel_stat.h | 11 +++++ kernel/sched/cputime.c | 82 +++++++++++++++++++++++++++++++++++++ 2 files changed, 93 insertions(+) diff --git a/include/linux/kernel_stat.h b/include/linux/kernel_stat.h index 7ee2bb43b251..79781196eb25 100644 --- a/include/linux/kernel_stat.h +++ b/include/linux/kernel_stat.h @@ -78,6 +78,17 @@ static inline unsigned int kstat_cpu_irqs_sum(unsigned int cpu) return kstat_cpu(cpu).irqs_sum; } +#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN +extern u64 kcpustat_field(struct kernel_cpustat *kcpustat, + enum cpu_usage_stat usage, int cpu); +#else +static inline u64 kcpustat_field(struct kernel_cpustat *kcpustat, + enum cpu_usage_stat usage, int cpu) +{ + return kcpustat->cpustat[usage]; +} +#endif + extern void account_user_time(struct task_struct *, u64); extern void account_guest_time(struct task_struct *, u64); extern void account_system_time(struct task_struct *, int, u64); diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index b931a19df093..e0cd20693ef5 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -911,4 +911,86 @@ void task_cputime(struct task_struct *t, u64 *utime, u64 *stime) *utime += vtime->utime + delta; } while (read_seqcount_retry(&vtime->seqcount, seq)); } + +static int kcpustat_field_vtime(u64 *cpustat, + struct vtime *vtime, + enum cpu_usage_stat usage, + int cpu, u64 *val) +{ + unsigned int seq; + int err; + + do { + seq = read_seqcount_begin(&vtime->seqcount); + + /* + * We raced against context switch, fetch the + * kcpustat task again. + */ + if (vtime->cpu != cpu && vtime->cpu != -1) + return -EAGAIN; + + /* + * Two possible things here: + * 1) We are seeing the scheduling out task (prev) or any past one. + * 2) We are seeing the scheduling in task (next) but it hasn't + * passed though vtime_task_switch() yet so the pending + * cputime of the prev task may not be flushed yet. + * + * Case 1) is ok but 2) is not. So wait for a safe VTIME state. + */ + if (vtime->state == VTIME_INACTIVE) + return -EAGAIN; + + err = 0; + + *val = cpustat[usage]; + + if (vtime->state == VTIME_SYS) + *val += vtime->stime + vtime_delta(vtime); + + } while (read_seqcount_retry(&vtime->seqcount, seq)); + + return 0; +} + +u64 kcpustat_field(struct kernel_cpustat *kcpustat, + enum cpu_usage_stat usage, int cpu) +{ + u64 *cpustat = kcpustat->cpustat; + struct rq *rq; + u64 val; + int err; + + if (!vtime_accounting_enabled_cpu(cpu)) + return cpustat[usage]; + + /* Only support sys vtime for now */ + if (usage != CPUTIME_SYSTEM) + return cpustat[usage]; + + rq = cpu_rq(cpu); + + for (;;) { + struct task_struct *curr; + struct vtime *vtime; + + rcu_read_lock(); + curr = rcu_dereference(rq->curr); + if (WARN_ON_ONCE(!curr)) { + rcu_read_unlock(); + return cpustat[usage]; + } + + vtime = &curr->vtime; + err = kcpustat_field_vtime(cpustat, vtime, usage, cpu, &val); + rcu_read_unlock(); + + if (!err) + return val; + + cpu_relax(); + } +} +EXPORT_SYMBOL_GPL(kcpustat_field); #endif /* CONFIG_VIRT_CPU_ACCOUNTING_GEN */ -- 2.23.0