From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 5D01A1DF738 for ; Mon, 6 Jan 2025 21:24:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736198697; cv=none; b=i+kye1MwOfzlzRM2ES6RG8eS5PO+ciT5t40Fl49NXQCdnzNNhpm0ESPpbi8eGgxkVZ51zL2DPRjXJVW8u+jxJ5BYKn7voLaRMr5tdRTvn4s1LWUPFKwrnn1/LOkgtwjQ50ie0YY6RDTI0FAvn4Hi98cEJw6hztlR5JR2rCztYnk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736198697; c=relaxed/simple; bh=19LBShY/LmVQoT1aeMiI1Yi9FXiopk1vv7ZTod1yKX4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=CtNiO+GK2zui5ahQ2DTK8xo2nNhEDv/7Xxy41iQslnqf6afxiLWjk7i94Glf9TJ2JYrXCArbQqqWet5gM2H90xYASsQzv6eZCzqkk5md2uHWvcNo290AV/yuF+lRZlQBtaLdOLd/7WvRgs19m5dL1iV7X3KeAyebkUv3sxjUPQk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=kd0ZLs9l; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="kd0ZLs9l" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 896D2C4CED2; Mon, 6 Jan 2025 21:24:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1736198696; bh=19LBShY/LmVQoT1aeMiI1Yi9FXiopk1vv7ZTod1yKX4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=kd0ZLs9ldy0OIR5H08OJHOCnXvyNUVnWFbsFYeXr8AlD2JlOxTfNts2un/z5hvjTG rYLcG7ikHThV9FpLSsMWpFWD1SBgoIqKbYC2aPK2Z3FapGp5Kxom041SOGwy/b/5GR EqsNqUzOp4zej6fijIYedacbcssEZhDdr1oGtFkLP8MlOoHX4VsBxMobica963/PLG N0g7IByYN7aa4NcdpHu5324Ph85Hl5MgsnsLoFoR+8nEIMH+Uzoimwa4BUWYvgZrSb YK+3cJ4xgFRTIcRkh0dvT5DUn6ixsKmN78H0e8u/O06KJlHRZ7lMvJINJrzN9NkeOT G01EYbm3MpDKg== Date: Mon, 6 Jan 2025 22:24:54 +0100 From: Frederic Weisbecker To: Costa Shulyupin Cc: linux-kernel@vger.kernel.org, Waiman Long Subject: Re: [RFC PATCH v1] stop_machine: Add stop_housekeeping_cpuslocked() Message-ID: References: <20241218171531.2217275-1-costa.shul@redhat.com> <20241218172754.GP2354@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Le Mon, Jan 06, 2025 at 03:08:11PM +0200, Costa Shulyupin a écrit : > On Wed, 18 Dec 2024 at 19:38, Frederic Weisbecker wrote: > > And so given the cost of such analysis and resulting possible patches, here > > is an important question: is it worth the effort? What is the usecase of > > shutting down a CPU while other isolated CPUs run critical isolated stuff? > > The goal is to implement dynamic CPU isolation for realtime tasks such as DPDK. > > Thomas Gleixner in https://lore.kernel.org/lkml/87bjz2210r.ffs@tglx/ suggested: > "CPU hotplug solves this problem without any hackery. Take a CPU offline, > change the mask of that CPU and bring it online again. Repeat until all > CPU changes are done." > > Unfortunately, CPU HP interferes with realtime tests and is > unsuitable for dynamic CPU isolation. > > Meanwhile, the maximum number of hyperthreads is climbing to 1024, > increasing the demand for CPU HP. I must confess I don't understand well your constraints. Why would you change the set of isolated CPUs while running realtime tests (btw. did you mean "tasks"?). Do I understand it correctly that your server may run different kinds of workloads concurrently, some of them isolated and some of them not, and these workloads may be added / removed concurrently _anytime_? And therefore a newly added isolated workload (which then adds CPUs to the isolated set) mustn't disturb unrelated already running isolated workloads? When you refer to realtime tasks, do you mean isolated? Thanks. > > Thank you, > Costa >