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=-7.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=no 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 EA879C433E3 for ; Tue, 25 Aug 2020 18:46:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D37A820738 for ; Tue, 25 Aug 2020 18:46:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Ifb0ZO37" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726825AbgHYSq3 (ORCPT ); Tue, 25 Aug 2020 14:46:29 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:30010 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726180AbgHYSqZ (ORCPT ); Tue, 25 Aug 2020 14:46:25 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1598381183; 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=yv62KVZ2y8sIUWkWiUl26dzjgg8e6IxrYk2AS4k3VmM=; b=Ifb0ZO37eTQdTHn2/5svcE8/YP+QBb0FohTPXX29T80gjxOkyinMk9SaAvoN4oq/LyrC/2 iNrredK8SzEZrLMO7eKIVfrh9rt3yo9B/tDFiVBKSpbBt5EJFvIuWEdgRNCNg5fqjqBaNg SeBNjZ2QdXI5YvrXcm7jSEtzVuIKAHQ= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-197-RdUUoSWtNj-ovDDyvBqtLg-1; Tue, 25 Aug 2020 14:46:21 -0400 X-MC-Unique: RdUUoSWtNj-ovDDyvBqtLg-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id B7B3E100854F; Tue, 25 Aug 2020 18:46:20 +0000 (UTC) Received: from fuller.cnet (ovpn-112-10.gru2.redhat.com [10.97.112.10]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3FBD25C1C2; Tue, 25 Aug 2020 18:46:20 +0000 (UTC) Received: by fuller.cnet (Postfix, from userid 1000) id 36099409D608; Tue, 25 Aug 2020 15:44:50 -0300 (-03) Message-ID: <20200825184414.442457749@fuller.cnet> User-Agent: quilt/0.66 Date: Tue, 25 Aug 2020 15:41:48 -0300 From: Marcelo Tosatti To: Frederic Weisbecker Cc: linux-kernel@vger.kernel.org, Marcelo Tosatti Subject: [patch 1/2] nohz: try to avoid IPI when configuring per-CPU posix timer References: <20200825184147.948670309@fuller.cnet> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When enabling per-CPU posix timers, an IPI to nohz_full CPUs might be performed (to re-read the dependencies and possibly not re-enter nohz_full on a given CPU). A common case is for applications that run on nohz_full= CPUs to not use POSIX timers (eg DPDK). This patch skips the IPI in case the task allowed mask does not intersect with nohz_full= CPU mask, when going through tick_nohz_dep_set_signal. This reduces interruptions to nohz_full= CPUs. Signed-off-by: Marcelo Tosatti --- include/linux/tick.h | 11 +++++++---- kernel/time/posix-cpu-timers.c | 4 ++-- kernel/time/tick-sched.c | 27 +++++++++++++++++++++++++-- 3 files changed, 34 insertions(+), 8 deletions(-) Index: linux-2.6/include/linux/tick.h =================================================================== --- linux-2.6.orig/include/linux/tick.h +++ linux-2.6/include/linux/tick.h @@ -207,7 +207,8 @@ extern void tick_nohz_dep_set_task(struc enum tick_dep_bits bit); extern void tick_nohz_dep_clear_task(struct task_struct *tsk, enum tick_dep_bits bit); -extern void tick_nohz_dep_set_signal(struct signal_struct *signal, +extern void tick_nohz_dep_set_signal(struct task_struct *tsk, + struct signal_struct *signal, enum tick_dep_bits bit); extern void tick_nohz_dep_clear_signal(struct signal_struct *signal, enum tick_dep_bits bit); @@ -252,11 +253,12 @@ static inline void tick_dep_clear_task(s if (tick_nohz_full_enabled()) tick_nohz_dep_clear_task(tsk, bit); } -static inline void tick_dep_set_signal(struct signal_struct *signal, +static inline void tick_dep_set_signal(struct task_struct *tsk, + struct signal_struct *signal, enum tick_dep_bits bit) { if (tick_nohz_full_enabled()) - tick_nohz_dep_set_signal(signal, bit); + tick_nohz_dep_set_signal(tsk, signal, bit); } static inline void tick_dep_clear_signal(struct signal_struct *signal, enum tick_dep_bits bit) @@ -284,7 +286,8 @@ static inline void tick_dep_set_task(str enum tick_dep_bits bit) { } static inline void tick_dep_clear_task(struct task_struct *tsk, enum tick_dep_bits bit) { } -static inline void tick_dep_set_signal(struct signal_struct *signal, +static inline void tick_dep_set_signal(struct task_struct *tsk, + struct signal_struct *signal, enum tick_dep_bits bit) { } static inline void tick_dep_clear_signal(struct signal_struct *signal, enum tick_dep_bits bit) { } Index: linux-2.6/kernel/time/posix-cpu-timers.c =================================================================== --- linux-2.6.orig/kernel/time/posix-cpu-timers.c +++ linux-2.6/kernel/time/posix-cpu-timers.c @@ -523,7 +523,7 @@ static void arm_timer(struct k_itimer *t if (CPUCLOCK_PERTHREAD(timer->it_clock)) tick_dep_set_task(p, TICK_DEP_BIT_POSIX_TIMER); else - tick_dep_set_signal(p->signal, TICK_DEP_BIT_POSIX_TIMER); + tick_dep_set_signal(p, p->signal, TICK_DEP_BIT_POSIX_TIMER); } /* @@ -1358,7 +1358,7 @@ void set_process_cpu_timer(struct task_s if (*newval < *nextevt) *nextevt = *newval; - tick_dep_set_signal(tsk->signal, TICK_DEP_BIT_POSIX_TIMER); + tick_dep_set_signal(tsk, tsk->signal, TICK_DEP_BIT_POSIX_TIMER); } static int do_cpu_nanosleep(const clockid_t which_clock, int flags, Index: linux-2.6/kernel/time/tick-sched.c =================================================================== --- linux-2.6.orig/kernel/time/tick-sched.c +++ linux-2.6/kernel/time/tick-sched.c @@ -302,6 +302,27 @@ static void tick_nohz_dep_set_all(atomic } /* + * Set bit on nohz full dependency, kicking all cpus + * only if task can run on nohz full CPUs. + */ +static void tick_nohz_dep_set_all_cond(struct task_struct *tsk, + atomic_t *dep, + enum tick_dep_bits bit) +{ + int prev; + unsigned long flags; + + prev = atomic_fetch_or(BIT(bit), dep); + if (prev) + return; + + raw_spin_lock_irqsave(&tsk->pi_lock, flags); + if (cpumask_intersects(&tsk->cpus_mask, tick_nohz_full_mask)) + tick_nohz_full_kick_all(); + raw_spin_unlock_irqrestore(&tsk->pi_lock, flags); +} + +/* * Set a global tick dependency. Used by perf events that rely on freq and * by unstable clock. */ @@ -382,9 +403,11 @@ EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_ta * Set a per-taskgroup tick dependency. Posix CPU timers need this in order to elapse * per process timers. */ -void tick_nohz_dep_set_signal(struct signal_struct *sig, enum tick_dep_bits bit) +void tick_nohz_dep_set_signal(struct task_struct *tsk, + struct signal_struct *sig, + enum tick_dep_bits bit) { - tick_nohz_dep_set_all(&sig->tick_dep_mask, bit); + tick_nohz_dep_set_all_cond(tsk, &sig->tick_dep_mask, bit); } void tick_nohz_dep_clear_signal(struct signal_struct *sig, enum tick_dep_bits bit)