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=-3.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,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 22A00C388F7 for ; Tue, 10 Nov 2020 13:04:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id ACD5020797 for ; Tue, 10 Nov 2020 13:03:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Wb0kyjvf" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731187AbgKJND6 (ORCPT ); Tue, 10 Nov 2020 08:03:58 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47098 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727536AbgKJND5 (ORCPT ); Tue, 10 Nov 2020 08:03:57 -0500 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BB6D6C0613CF for ; Tue, 10 Nov 2020 05:03:57 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=fp7D+Rk1gLctsTUwetXl8upRlcZipYf0vD5R4+hKV0M=; b=Wb0kyjvffOMslQMoTbAl+UlVaX 0aWnay1Ll8eC01J959isieyKksAa8ZQRfrda8aP6KjB098GDWGLhpR7mIQO6GUiGBxv1Z9beXVD7I zqzts4RtXpVOwgHHkXY7vrWWaBx5Lza89PPh0HXI9schtfRIoBpUV8J/YD8sMYIYi9MXUodq+pzir ynRzukDMGnfnGy26eQv0T8/jmUwujxBp9tv6dxtsKGpWx/lX61WmcbXotX1qQpk788r0BJVbxMkrs ys5TGlDx8ILat9+/qfjPk0ho/n+H5BTQrzD7rQSEi+CjBFmkrnzv/XlCFbMr2FU5fc4Q1sLrVs186 NfdNF87A==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kcTJO-0002Xd-Or; Tue, 10 Nov 2020 13:03:51 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 1307A301E02; Tue, 10 Nov 2020 14:03:49 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id E5B952BA1DD1B; Tue, 10 Nov 2020 14:03:48 +0100 (CET) Date: Tue, 10 Nov 2020 14:03:48 +0100 From: Peter Zijlstra To: Valentin Schneider Cc: Marc Zyngier , LAK , linux-kernel , Will Deacon , Catalin Marinas , Thomas Gleixner , Android Kernel Team Subject: Re: [PATCH 0/2] arm64: Allow the rescheduling IPI to bypass irq_enter/exit Message-ID: <20201110130348.GK2594@hirez.programming.kicks-ass.net> References: <20201101131430.257038-1-maz@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 02, 2020 at 10:30:50AM +0000, Valentin Schneider wrote: > Now, I'd like to pen exactly why we think it's okay to forgo irq_{enter, > exit}() for that one IRQ and not any other. Thomas already said a few words on this, but basically scheduler_ipi() is a NOP (*almost*), the IPI has no body. All it does is tickle the return-from-interrupt path. So any setup and tear-down done for the non-existing body is a waste of time.