From nobody Mon Feb 9 12:24:08 2026 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C3086126BF3 for ; Sat, 21 Sep 2024 19:08:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726945687; cv=none; b=RLTzU0ZiQHazxU+9viM+wzv/lAxpNn+GHrZfUFtJ9PtuS0WkUbPAmzO4D5aAqk5DJrIUXK9ZbWAfFvshuJAUD9BKtJlpgZU0UGJEyWvtKpZZWYwsIvAjwFeDqr9g3+D5epssejhDoff2VIYMo/4yuKkvv8qf0MpwdqNCIfiT/7Q= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1726945687; c=relaxed/simple; bh=VQeNTpXMIwAp46t86U24dnCwflvwKJxs+ep3wJU+cj0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=oczdLGRCEzQJmYMm7IKf/HDZgBfaAKYDl3RhXFVMP2UENClz8zPwRRFfwmEmfsZegArBCZZrga2JdEVvNE3+hwNKgL+NNSto+yxw5tnOxkykXaNa/KcyAm83hJWnVQM8y0ZPUIle/k8iBaYn9fkD6QWOhI0pca1d9pkOxOw2b4Y= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=DJpSZAkt; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="DJpSZAkt" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1726945684; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=TgVcm3Qd2yD7/d4w7weoF1xnG5k0KKeLeGB66utTa4g=; b=DJpSZAktWF4KEI0DIu0aFWPHlNfL7/6+bW0RWI55SDF9jzKDWPp0HfWKxJugUwDBrhGsWn mWyIVWztQu/mEiSqEp/k5pi5VHLxDG5DPeGpdarLPe7Jkmy5EECO6p5tWG3coOB2JH+zBe zgyrx2WLz6FT1v+eqt8lQJ+z9GhFQAw= Received: from mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-651-_2XP1_9BNFGVHI8Sc1_a2A-1; Sat, 21 Sep 2024 15:08:01 -0400 X-MC-Unique: _2XP1_9BNFGVHI8Sc1_a2A-1 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (unknown [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id CDEA5192E27C; Sat, 21 Sep 2024 19:07:59 +0000 (UTC) Received: from llong.com (unknown [10.45.224.27]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 9650219560AB; Sat, 21 Sep 2024 19:07:55 +0000 (UTC) From: Waiman Long To: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , Frederic Weisbecker Cc: linux-kernel@vger.kernel.org, Phil Auld , Waiman Long Subject: [PATCH v4 2/4] sched/isolation: Make "isolcpus=nohz" equivalent to "nohz_full" Date: Sat, 21 Sep 2024 15:07:18 -0400 Message-ID: <20240921190720.106195-3-longman@redhat.com> In-Reply-To: <20240921190720.106195-1-longman@redhat.com> References: <20240921190720.106195-1-longman@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Content-Type: text/plain; charset="utf-8" The "isolcpus=3Dnohz" boot parameter and flag were used to disable tick when running a single task. Nowsdays, this "nohz" flag is seldomly used as it is included as part of the "nohz_full" parameter. Extend this flag to cover other kernel noises disabled by the "nohz_full" parameter to make them equivalent. This also eliminates the need to use both the "isolcpus" and the "nohz_full" parameters to fully isolated a given set of CPUs. Suggested-by: Frederic Weisbecker Signed-off-by: Waiman Long Acked-by: Frederic Weisbecker --- Documentation/admin-guide/kernel-parameters.txt | 4 +++- kernel/sched/isolation.c | 6 +++++- 2 files changed, 8 insertions(+), 2 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentatio= n/admin-guide/kernel-parameters.txt index 8337d0fed311..4e664587943f 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2424,7 +2424,9 @@ specified in the flag list (default: domain): =20 nohz - Disable the tick when a single task runs. + Disable the tick when a single task runs as well as + disabling other kernel noises like having RCU callbacks + offloaded. This is equivalent to the nohz_full parameter. =20 A residual 1Hz tick is offloaded to workqueues, which you need to affine to housekeeping through the global diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c index 5345e11f3d44..6a686322ce3c 100644 --- a/kernel/sched/isolation.c +++ b/kernel/sched/isolation.c @@ -209,9 +209,13 @@ static int __init housekeeping_isolcpus_setup(char *st= r) int len; =20 while (isalpha(*str)) { + /* + * isolcpus=3Dnohz is equivalent to nohz_full. + */ if (!strncmp(str, "nohz,", 5)) { str +=3D 5; - flags |=3D HK_FLAG_TICK; + flags |=3D HK_FLAG_TICK | HK_FLAG_WQ | HK_FLAG_TIMER | + HK_FLAG_RCU | HK_FLAG_MISC | HK_FLAG_KTHREAD; continue; } =20 --=20 2.43.5