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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 22E8DC433FE for ; Tue, 26 Oct 2021 14:11:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 044F26103C for ; Tue, 26 Oct 2021 14:11:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236435AbhJZONa (ORCPT ); Tue, 26 Oct 2021 10:13:30 -0400 Received: from mail.kernel.org ([198.145.29.99]:40650 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236431AbhJZON2 (ORCPT ); Tue, 26 Oct 2021 10:13:28 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 13ACB61090; Tue, 26 Oct 2021 14:11:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1635257464; bh=FyBqhCDkTOSwhGAqCQeLfGAKiuUaKIxcmf4jS04tKSI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=A/PwOGg3nRhm1yKxCbKqfBxpBUrnyTP5T3xurHrkaOKjrWCKgHS7PeV2420qdJ3hi JotzzX91yArW4aA8i0mtDS/zIvYfoKOE8l++N/k+rl4CHs8YVC6RQu/OABrC92jL3P jf2834D3vtBN/DLqagV0n5lBMapCkXbRLuJyadhyd0LgSAXT0uYG8eanuI+xAzwcnn tePhOFpdCMpjBRsDC6Hua/FaB6a5+2g/dvgyaCIMlXlh0LLgLupQhIFmIYj+zSx0bM NjU2NT/keiXH6OAeWpXo+aENGg9PeUNFyEqT7VGG8BJAw8ufEs+pGac3hkKfEgAKIS K4l+3OUcu5bKw== From: Frederic Weisbecker To: Thomas Gleixner Cc: LKML , Frederic Weisbecker , Peter Zijlstra , Hasegawa Hitomi , Mel Gorman Subject: [PATCH 2/2] sched/cputime: Fix getrusage(RUSAGE_THREAD) with nohz_full Date: Tue, 26 Oct 2021 16:10:55 +0200 Message-Id: <20211026141055.57358-3-frederic@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20211026141055.57358-1-frederic@kernel.org> References: <20211026141055.57358-1-frederic@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org getrusage(RUSAGE_THREAD) with nohz_full may return shorter utime/stime than the actual time. task_cputime_adjusted() snapshots utime and stime and then adjust their sum to match the scheduler maintained cputime.sum_exec_runtime. Unfortunately in nohz_full, sum_exec_runtime is only updated once per second in the worst case, causing a discrepancy against utime and stime that can be updated anytime by the reader using vtime. To fix this situation, perform an update of cputime.sum_exec_runtime when the cputime snapshot reports the task as actually running while the tick is disabled. The related overhead is then contained within the relevant situations. Reported-by: Hasegawa Hitomi Signed-off-by: Frederic Weisbecker Cc: Mel Gorman Cc: Peter Zijlstra Signed-off-by: Hasegawa Hitomi --- include/linux/sched/cputime.h | 5 +++-- kernel/sched/cputime.c | 12 +++++++++--- 2 files changed, 12 insertions(+), 5 deletions(-) diff --git a/include/linux/sched/cputime.h b/include/linux/sched/cputime.h index 6c9f19a33865..ce3c58286062 100644 --- a/include/linux/sched/cputime.h +++ b/include/linux/sched/cputime.h @@ -18,15 +18,16 @@ #endif /* CONFIG_VIRT_CPU_ACCOUNTING_NATIVE */ #ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN -extern void task_cputime(struct task_struct *t, +extern bool task_cputime(struct task_struct *t, u64 *utime, u64 *stime); extern u64 task_gtime(struct task_struct *t); #else -static inline void task_cputime(struct task_struct *t, +static inline bool task_cputime(struct task_struct *t, u64 *utime, u64 *stime) { *utime = t->utime; *stime = t->stime; + return false; } static inline u64 task_gtime(struct task_struct *t) diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index 872e481d5098..9392aea1804e 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -615,7 +615,8 @@ void task_cputime_adjusted(struct task_struct *p, u64 *ut, u64 *st) .sum_exec_runtime = p->se.sum_exec_runtime, }; - task_cputime(p, &cputime.utime, &cputime.stime); + if (task_cputime(p, &cputime.utime, &cputime.stime)) + cputime.sum_exec_runtime = task_sched_runtime(p); cputime_adjust(&cputime, &p->prev_cputime, ut, st); } EXPORT_SYMBOL_GPL(task_cputime_adjusted); @@ -828,19 +829,21 @@ u64 task_gtime(struct task_struct *t) * add up the pending nohz execution time since the last * cputime snapshot. */ -void task_cputime(struct task_struct *t, u64 *utime, u64 *stime) +bool task_cputime(struct task_struct *t, u64 *utime, u64 *stime) { struct vtime *vtime = &t->vtime; unsigned int seq; u64 delta; + int ret; if (!vtime_accounting_enabled()) { *utime = t->utime; *stime = t->stime; - return; + return false; } do { + ret = false; seq = read_seqcount_begin(&vtime->seqcount); *utime = t->utime; @@ -850,6 +853,7 @@ void task_cputime(struct task_struct *t, u64 *utime, u64 *stime) if (vtime->state < VTIME_SYS) continue; + ret = true; delta = vtime_delta(vtime); /* @@ -861,6 +865,8 @@ void task_cputime(struct task_struct *t, u64 *utime, u64 *stime) else *utime += vtime->utime + delta; } while (read_seqcount_retry(&vtime->seqcount, seq)); + + return ret; } static int vtime_state_fetch(struct vtime *vtime, int cpu) -- 2.25.1