From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-98.freemail.mail.aliyun.com (out30-98.freemail.mail.aliyun.com [115.124.30.98]) (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 770B1429029; Thu, 15 Oct 2026 17:48:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.98 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792086538; cv=none; b=J3bxp+b+ujevT7xjV8GPjuAK6tqUFJUO8YL/+vYnQiQQCWFIojgf1ZzFmuRDVwXS14Q7E4cxuA9E6h+IbMMz/9PGhoOZBkozgSHBgWGF1Op78Vi2zRcMBJCUKk4LgFv9jyUcvUkz9YPk44DfHhbPqUn6EBze+5ltDj9yny0Zmy4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792086538; c=relaxed/simple; bh=9c2/PaGf1u2yPgJLZdE2wgl/BvhUgfPpxVWHX6kIGWE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=QUuRo5ro/GvtJ6tDFcVkseGDUf/bhwGk5yUlqMklh9NzBia8PSAI4zUJdw9/A3XjAAy2eV/T6ZweO3EeHyUEATWTdg0RIQ9D39j72b9jUCuFL993PckVRR9VNiT5O6uXvhdneeuZWQ+DXFFVQCDtkVm7L/Zwo3rg9QTZiMxem4w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=SRkneZY7; arc=none smtp.client-ip=115.124.30.98 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="SRkneZY7" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1792086514; h=Date:From:To:Subject:Message-ID:MIME-Version:Content-Type; bh=dkulAnttC6PoebpWm1nHtQ7Lp9yXSkyxV6VmIgyOjW0=; b=SRkneZY7+Rt1Y2x6YqysYgUlJffnd/7uYUPzsJ3JFZNyI4FD33ShjSUkSCX8gM72rkIOAoZyya6pOlnUYWZJfvkmen5TAT/pV2Bsl6ZPJ2Ec94peVm10ccpkNioSOtMj5bBWRhsBq5lWxTyIKw2HEAi1nLFibI1VBCc6CvD1maw= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R221e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033037033178;MF=peng_wang@linux.alibaba.com;NM=1;PH=DS;RN=19;SR=0;TI=SMTPD_---0XCsGuGY_1792086512; Received: from localhost(mailfrom:peng_wang@linux.alibaba.com fp:SMTPD_---0XCsGuGY_1792086512 cluster:ay36) by smtp.aliyun-inc.com; Fri, 16 Oct 2026 01:48:33 +0800 Date: Fri, 16 Oct 2026 01:48:32 +0800 From: Peng Wang To: Waiman Long Cc: Anna-Maria Behnsen , Frederic Weisbecker , Ingo Molnar , Thomas Gleixner , Greg Kroah-Hartman , "Rafael J . Wysocki" , Danilo Krummrich , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Peter Zijlstra , Tejun Heo , He Rongguang , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, driver-core@lists.linux.dev, linux-trace-kernel@vger.kernel.org, cgroups@vger.kernel.org Subject: Re: [RFC PATCH 0/2] tick/nohz: Add runtime control of non-idle tick suppression Message-ID: Reply-To: Peng Wang References: <8d10bb84-d312-4be0-8c43-ddd602850a1d@redhat.com> Precedence: bulk X-Mailing-List: linux-api@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8d10bb84-d312-4be0-8c43-ddd602850a1d@redhat.com> On Thu, Oct 15, 2026 at 12:00:25PM -0400, Waiman Long wrote: > On 10/15/26 8:43 AM, Peng Wang wrote: > > Workloads and their need for periodic ticks can change after boot. > > This series lets userspace choose at runtime which CPUs in the boot-time > > nohz_full set retain the non-idle scheduler tick and which are permitted > > to stop it, while preserving the existing isolation configuration. > > > > The first patch adds a per-CPU tick dependency; the second exposes a > > sysfs CPU list. Permission defaults to all nohz_full CPUs. Revocation > > uses the existing asynchronous kick. Idle tick suppression is unchanged, > > and policy persists across hotplug. > So you are basically setting up more nohz_full CPUs than the system actually > needs to use at the moment and so want to disable nohz/tick part of > nohz_full CPUs that don't need it. Can you elaborate more about the problems > solve by introducing this new behavior? Hi Waiman, Yes. We have CPU-pinned workloads that benefit from reduced periodic tick interference. The desired tick policy changes with CPU allocation. With spare capacity, we allow selected nohz_full CPUs to stop their tick. When capacity is fully allocated, we prefer to retain the non-idle periodic tick across CPUs, avoiding an additional difference in tick interference between housekeeping and nohz_full CPUs. A CPU may still have only one runnable task in either case, so the existing tick dependencies do not express this policy. This series keeps the boot-time nohz_full CPU set, context tracking, RCU offloading and housekeeping configuration unchanged. It only controls whether those CPUs may stop their non-idle tick. The policy can be changed without taking CPUs offline. > > > > Existing cpuset partition modes do not express this independent tick > > policy. Feedback on the proposed interface is welcome. > > We are planning to eventually extend cpuset partition mode to change > nohz_full at runtime. This is still a work in progress. Thanks for mentioning the cpuset work. Would this tick-only policy fit into that plan? The core mechanism in patch 1 is independent of the sysfs interface. Thanks, Peng > > Regards, > Longman > > > > > Thanks, > > Peng > > > > Peng Wang (2): > > tick/nohz: Add a policy dependency for full dynticks > > cpu: Add sysfs control of full dynticks policy > > > > .../ABI/testing/sysfs-devices-system-cpu | 40 ++++++++++++ > > drivers/base/cpu.c | 46 ++++++++++++++ > > include/linux/tick.h | 8 ++- > > include/trace/events/timer.h | 3 +- > > kernel/time/tick-sched.c | 62 +++++++++++++++++++ > > 5 files changed, 156 insertions(+), 3 deletions(-) > > > > > > base-commit: 0fcb05b72344f40806cbe810de8872f1698bf053 >