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 03E2AC54EE9 for ; Wed, 28 Sep 2022 13:01:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233600AbiI1NBT (ORCPT ); Wed, 28 Sep 2022 09:01:19 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56740 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233785AbiI1NBF (ORCPT ); Wed, 28 Sep 2022 09:01:05 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 965DF9DB4F for ; Wed, 28 Sep 2022 06:00:47 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A1A191063; Wed, 28 Sep 2022 06:00:53 -0700 (PDT) Received: from wubuntu (unknown [10.57.34.4]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9CD1C3F73D; Wed, 28 Sep 2022 06:00:44 -0700 (PDT) Date: Wed, 28 Sep 2022 14:00:43 +0100 From: Qais Yousef To: John Stultz Cc: LKML , John Dias , Connor O'Brien , Rick Yiu , John Kacur , Chris Redpath , Abhijeet Dharmapurikar , Peter Zijlstra , Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Thomas Gleixner , Heiko Carstens , Vasily Gorbik , kernel-team@android.com Subject: Re: [RFC][PATCH v3 0/3] Softirq -rt Optimizations Message-ID: <20220928130043.d6ijyxbq43tfvqg7@wubuntu> References: <20220921012550.3288570-1-jstultz@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220921012550.3288570-1-jstultz@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi John On 09/21/22 01:25, John Stultz wrote: > Hey all, > > This series is a set of patches that optimize scheduler decisions around > realtime tasks and softirqs. This series is a rebased and reworked set > of changes that have been shipping on Android devices for a number of > years, originally created to resolve audio glitches seen on devices > caused by softirqs for network or storage drivers. > > Long running softirqs cause issues because they aren’t currently taken > into account when a realtime task is woken up, but they will delay > realtime tasks from running if the realtime tasks are placed on a cpu > currently running a softirq. Thanks a lot for sending this series. I've raised this problem in various venues in the past, but it seems it is hard to do something better than what you propose here. Borrowing some behaviours from PREEMPT_RT (like threadedirqs) won't cut it outside PREEMPT_RT AFAIU. Peter did suggest an alternative at one point in the past to be more aggressive in limiting softirqs [1] but I never managed to find the time to verify it - especially its impact on network throughput as this seems to be the tricky trade-of (and tricky thing to verify for me at least). I'm not sure if BLOCK softirqs are as sensitive. I think the proposed approach is not intrusive and offers a good balance that is well contained and easy to improve upon on the future. It's protected with a configuration option so users that don't want it can easily disable it. [1] https://gitlab.arm.com/linux-arm/linux-qy/-/commits/core/softirq/ Thanks -- Qais Yousef