From nobody Wed Sep 17 08:45:04 2025 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C001BC4167B for ; Wed, 21 Dec 2022 17:12:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234855AbiLURMP (ORCPT ); Wed, 21 Dec 2022 12:12:15 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53200 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234745AbiLURLf (ORCPT ); Wed, 21 Dec 2022 12:11:35 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 61EE330D for ; Wed, 21 Dec 2022 09:10:53 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1671642652; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: references:references; bh=C7fcHUyzcW4F+ucufGFezQLMgXWfhaM9eBPMwThasic=; b=T/Mpt5XG6t2f00mHTtF7WURimWN7Fv1rArJ/EUkpY+1Ay286+MNlzKgRqGerxM8RourWxJ HIq1OnbVN+CvCMSlU66MTOrZIEEJtt8+KS5vx4ydleGDfQChU9ioYe5lESm+Io9iUhzYhN aklraXRwwzYPXoOcTzK2upMsPrMdbzo= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-25-i--luYGMNhq27CYJNt6lVw-1; Wed, 21 Dec 2022 12:10:45 -0500 X-MC-Unique: i--luYGMNhq27CYJNt6lVw-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 23A8B18E0045; Wed, 21 Dec 2022 17:10:45 +0000 (UTC) Received: from tpad.localdomain (ovpn-112-4.gru2.redhat.com [10.97.112.4]) by smtp.corp.redhat.com (Postfix) with ESMTPS id CADF8112132C; Wed, 21 Dec 2022 17:10:44 +0000 (UTC) Received: by tpad.localdomain (Postfix, from userid 1000) id A883040408D5D; Wed, 21 Dec 2022 14:09:34 -0300 (-03) Message-ID: <20221221170436.370028855@redhat.com> User-Agent: quilt/0.66 Date: Wed, 21 Dec 2022 13:58:05 -0300 From: Marcelo Tosatti To: atomlin@atomlin.com, frederic@kernel.org Cc: cl@linux.com, tglx@linutronix.de, mingo@kernel.org, peterz@infradead.org, pauld@redhat.com, neelx@redhat.com, oleksandr@natalenko.name, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Marcelo Tosatti Subject: [PATCH v11 4/6] tick/nohz_full: Ensure quiet_vmstat() is called on exit to user-mode when the idle tick is stopped References: <20221221165801.362118576@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Aaron Tomlin For nohz full CPUs, we'd like the per-CPU vm statistics to be synchronized when userspace is executing. Otherwise, the vmstat_shepherd might queue a work item to synchronize them, which is undesired intereference for isolated CPUs. This patch syncs CPU-specific vmstat differentials, on return to userspace, if CONFIG_FLUSH_WORK_ON_RESUME_USER is enabled and the tick is stopped. A trivial test program was used to determine the impact of the proposed changes and under vanilla. The mlock(2) and munlock(2) system calls was used solely to modify vmstat item 'NR_MLOCK'. The following is an average count of CPU-cycles across the aforementioned system calls: Vanilla Modified Cycles per syscall 8461 8690 (+2.6%) Signed-off-by: Aaron Tomlin Signed-off-by: Marcelo Tosatti --- include/linux/tick.h | 5 +++-- kernel/time/tick-sched.c | 15 +++++++++++++++ 2 files changed, 18 insertions(+), 2 deletions(-) Index: linux-2.6/include/linux/tick.h =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D --- linux-2.6.orig/include/linux/tick.h +++ linux-2.6/include/linux/tick.h @@ -11,7 +11,6 @@ #include #include #include -#include =20 #ifdef CONFIG_GENERIC_CLOCKEVENTS extern void __init tick_init(void); @@ -272,6 +271,7 @@ static inline void tick_dep_clear_signal =20 extern void tick_nohz_full_kick_cpu(int cpu); extern void __tick_nohz_task_switch(void); +void __tick_nohz_user_enter_prepare(void); extern void __init tick_nohz_full_setup(cpumask_var_t cpumask); #else static inline bool tick_nohz_full_enabled(void) { return false; } @@ -296,6 +296,7 @@ static inline void tick_dep_clear_signal =20 static inline void tick_nohz_full_kick_cpu(int cpu) { } static inline void __tick_nohz_task_switch(void) { } +static inline void __tick_nohz_user_enter_prepare(void) { } static inline void tick_nohz_full_setup(cpumask_var_t cpumask) { } #endif =20 @@ -308,7 +309,7 @@ static inline void tick_nohz_task_switch static inline void tick_nohz_user_enter_prepare(void) { if (tick_nohz_full_cpu(smp_processor_id())) - rcu_nocb_flush_deferred_wakeup(); + __tick_nohz_user_enter_prepare(); } =20 #endif Index: linux-2.6/kernel/time/tick-sched.c =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D --- linux-2.6.orig/kernel/time/tick-sched.c +++ linux-2.6/kernel/time/tick-sched.c @@ -26,6 +26,7 @@ #include #include #include +#include =20 #include =20 @@ -519,6 +520,22 @@ void __tick_nohz_task_switch(void) } } =20 +void __tick_nohz_user_enter_prepare(void) +{ + if (tick_nohz_full_cpu(smp_processor_id())) { +#ifdef CONFIG_FLUSH_WORK_ON_RESUME_USER + struct tick_sched *ts; + + ts =3D this_cpu_ptr(&tick_cpu_sched); + + if (ts->tick_stopped) + quiet_vmstat(true); +#endif + rcu_nocb_flush_deferred_wakeup(); + } +} +EXPORT_SYMBOL_GPL(__tick_nohz_user_enter_prepare); + /* Get the boot-time nohz CPU list from the kernel parameters. */ void __init tick_nohz_full_setup(cpumask_var_t cpumask) {