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 X-Spam-Level: X-Spam-Status: No, score=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 33F04C54FCC for ; Tue, 21 Apr 2020 14:09:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 12546206B9 for ; Tue, 21 Apr 2020 14:09:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587478180; bh=47dRdhfCGfscyToO3yQIR/h3qAEu9MIShpFMyDMcDmI=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=EH7Smk4ZhsN7MfedbpjjSBvZ7K21ovJ39F42ysWuRCj123RlYP7iWTdbHx582HsNf dM/0RNx8tq8HBek1no15xtbEmaKiLwVIs7lhm6vdTAmFtFgvCZvvU9KmzQ05IpIzBx qrQKrwFYuC6hqwB3akv9xzD4TWnSjU5CSZAvgitM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728651AbgDUOJj (ORCPT ); Tue, 21 Apr 2020 10:09:39 -0400 Received: from mail.kernel.org ([198.145.29.99]:33606 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728316AbgDUOJi (ORCPT ); Tue, 21 Apr 2020 10:09:38 -0400 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id AC31C20679; Tue, 21 Apr 2020 14:09:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587478177; bh=47dRdhfCGfscyToO3yQIR/h3qAEu9MIShpFMyDMcDmI=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=yFw/bG6wzQTTx41T7fqFE/rQqJQh+ZXKvwN8atl/NcYeL9chbqyoSJAH8F38mH+gq F7I99+ZbrVRFK+sSpqtfFJ9fRG8x1ZP61XCwnFYL50Sk3k2u7Yfn6VShMA08vaTpDZ 190GqcI/SyUD/BjsR16rZ4j5fqpbKO51eqOzt3mk= Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1jQtah-005Cye-Tb; Tue, 21 Apr 2020 15:09:36 +0100 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Tue, 21 Apr 2020 15:09:35 +0100 From: Marc Zyngier To: Valentin Schneider , Qais Yousef Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Andrew Morton , Thomas Gleixner , Yury Norov , Paul Turner , Alexey Dobriyan , Josh Don , Pavan Kondeti , linux-kernel@vger.kernel.org, "Rafael J. Wysocki" Subject: Re: [PATCH 0/4] sched/rt: Distribute tasks in find_lowest_rq() In-Reply-To: References: <20200414150556.10920-1-qais.yousef@arm.com> <20200421121305.ziu3dfqwo7cw6ymu@e107158-lin.cambridge.arm.com> Message-ID: X-Sender: maz@kernel.org User-Agent: Roundcube Webmail/1.3.10 X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: valentin.schneider@arm.com, qais.yousef@arm.com, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, akpm@linux-foundation.org, tglx@linutronix.de, yury.norov@gmail.com, pjt@google.com, adobriyan@gmail.com, joshdon@google.com, pkondeti@codeaurora.org, linux-kernel@vger.kernel.org, rjw@rjwysocki.net X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-04-21 14:18, Valentin Schneider wrote: > On 21/04/20 13:13, Qais Yousef wrote: [...] >> I CCed Marc who's the maintainer of this file who can clarify better >> if this >> really breaks anything. >> >> If any interrupt expects to be affined to a specific CPU then this >> must be >> described in DT/driver. I think the GIC controller is free to >> distribute them >> to any cpu otherwise if !force. Which is usually done by irq_balancer >> anyway >> in userspace, IIUC. >> >> I don't see how cpumask_any_and() break anything here too. I actually >> think it >> improves on things by better distribute the irqs on the system by >> default. That's a pretty bold statement. Unfortunately, it isn't universally true. Some workload will be very happy with interrupts spread all over the map, and some others will suffer from it because, well, it interrupts userspace. > As you say, if someone wants smarter IRQ affinity they can do > irq_balancer > and whatnot. The default kernel policy for now has been to shove > everything > on the lowest-numbered CPU, and I see no valid reason to change that. Exactly. I would like to keep the kernel policy as simple as possible for non-managed interrupts (managed interrupts are another kettle of fish entirely). Userpace is in control to place things "intelligently", so let's not try and make the kernel smarter than it strictly needs to be. Thanks, M. -- Jazz is not dead. It just smells funny...