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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4098BC4332F for ; Tue, 12 Dec 2023 13:28:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232470AbjLLN2L (ORCPT ); Tue, 12 Dec 2023 08:28:11 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39632 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232783AbjLLN1y (ORCPT ); Tue, 12 Dec 2023 08:27:54 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7AED0F2 for ; Tue, 12 Dec 2023 05:27:59 -0800 (PST) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A46B0C433C7; Tue, 12 Dec 2023 13:27:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1702387679; bh=A61JJ3QepchMq+n/hTd5+pCDDReFj7GC3GGL0Fy/B70=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=fZ79lRiYpPFSifS88bmIdqzYMk2u9yJzTZ5YDjGKQAqeIPuFqi/cUykVzdEfjJEr3 HGwBR/huZUCDaNiSo0MGDAD81Ts8ow3RgoZFHWRlw3aZQRuocakNw+aMmvegaVGTKx eCr3i+xwKcY4TWNbnJjGU+s5l3k5y1UTYCtURVICdIBlHYqK5gJvrnh7Uu3baVCuSa C6RZTGXf1ZawGLX0fbo938bWA/f+MykhCONd22BJqfbdvcKMm0rv337CLe37x3siRD Wf6RsIxZoGePOPoXScTnQyiMPFSi7j6n8ju05rhVmxYq9/HVyQX4IhO8K/rLeTmVxY 38iOk+lm6bzIA== Date: Tue, 12 Dec 2023 14:27:56 +0100 From: Frederic Weisbecker To: Gianfranco Dutka Cc: Waiman Long , Tejun Heo , Vincent Guittot , linux-kernel@vger.kernel.org, vincent.guittot@linaro.com, Ingo Molnar , Peter Zijlstra , Juri Lelli , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Valentin Schneider , "Pandruvada, Srinivas" Subject: Re: Modifying isolcpus, nohz_full, and rcu_nocb kernel parameters at runtime Message-ID: References: <76587DD3-2A77-41A3-9807-6AEE4398EBA6@arista.com> <25E6E1E4-DC16-490E-B907-A3236FB9317A@arista.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <25E6E1E4-DC16-490E-B907-A3236FB9317A@arista.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 08, 2023 at 09:18:53AM -0500, Gianfranco Dutka wrote: > > > The isolcpus, nohz_full and rcu_nocbs are boot-time kernel parameters. I am in the process of improving dynamic CPU isolation at runtime. Right now, we are able to do isolcpus=domain with the isolated cpuset partition functionality. Other aspects of CPU isolation are being looked at with the goal of reducing the gap of what one can do at boot time versus what can be done at run time. It will certain take time to reach that goal. > > > > Cheers, > > Longman > > > > Thank you Waiman for the response. It would seem that getting similar > functionality through cgroups/cpusets is the only option at the moment. Is it > completely out of the question to possibly patch the kernel to modify these > parameters at runtime? Or would that entail a significant change that might > not be so trivial to accomplish? For instance, the solution wouldn’t be as > simple as patching the kernel to make these writeable and then calling the > same functions which run at boot-time when these parameters are originally > written? As for nohz_full (which implies rcu_nocb), it's certainly possible to make it tunable at runtime via cpusets. If people really want it, I'm willing to help. Thanks.