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 C42F3C43457 for ; Fri, 9 Oct 2020 09:47:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5212C2225D for ; Fri, 9 Oct 2020 09:47:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="qHI4TdYN" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733238AbgJIJrv (ORCPT ); Fri, 9 Oct 2020 05:47:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37946 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725917AbgJIJrt (ORCPT ); Fri, 9 Oct 2020 05:47:49 -0400 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6B3E4C0613D2 for ; Fri, 9 Oct 2020 02:47:49 -0700 (PDT) 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=omMwUi1pb0JZYEzX9WrMwNVM/9noWra8skwW352I5FM=; b=qHI4TdYNEzWyfUfPt9MFUcGLDU ExiZiIRnUVS7ww5mj2B/4N/e4qtqL+eNIg32SPlGFQyoLEC981bFX4PbPBYjSfRnldTbCDFNUXIOI 8RYGYjAb8Kf+izUxecbZF6RF6gWuwFystKL69nyQ+Uc8a0BJX7C+F1CNMQyZ59ZnXoNRJf4tDCpXq 48GS9UeguOGZsw5fF6Kq4moA2qgpT6vTTZM2fHJublakBNyst+1SguQ58MQ/aNlXxrkbm5T5pxG6d PpLJnS4Zc4Wf5aoaBIUPDuNd7EOsKcySlTMTSLwnq4J+lGCYkwZUQVNmHlv8VlhFpUH5rQ80EIFK3 IIw5ArRQ==; 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 1kQp03-0004ws-Mf; Fri, 09 Oct 2020 09:47:43 +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 3A6A33019CE; Fri, 9 Oct 2020 11:47:41 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id D4F2320DB441C; Fri, 9 Oct 2020 11:47:41 +0200 (CEST) Date: Fri, 9 Oct 2020 11:47:41 +0200 From: Peter Zijlstra To: Michal Hocko Cc: Thomas Gleixner , Frederic Weisbecker , LKML , Mel Gorman , Ingo Molnar Subject: Re: [RFC PATCH] kernel: allow to configure PREEMPT_NONE, PREEMPT_VOLUNTARY on kernel command line Message-ID: <20201009094741.GH2628@hirez.programming.kicks-ass.net> References: <20201007120401.11200-1-mhocko@kernel.org> <20201007122144.GF2628@hirez.programming.kicks-ass.net> <20201007123553.GK29020@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201007123553.GK29020@dhcp22.suse.cz> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 07, 2020 at 02:35:53PM +0200, Michal Hocko wrote: > On Wed 07-10-20 14:21:44, Peter Zijlstra wrote: > > On Wed, Oct 07, 2020 at 02:04:01PM +0200, Michal Hocko wrote: > > > I wanted to make sure that the idea is sound for maintainers first. The > > > next step would be extending the command line to support full preemption > > > as well but there is much more work in that area. Frederic has promissed > > > to look into that. > > > > The sanest way there is to static_call() __preempt_schedule() I think. > > Yes, I have checked the code and identified few other places like > irqentry_exit_cond_resched. We also need unconditional > CONFIG_PREEMPT_COUNT IIUC and there are quite some places guarded by > CONFIG_PREEMPTION that would need to be examined. Some of them are > likely pretending to be more clever than they really are/should be - > e.g. mm/slub.c. So there is likely a lot of leg work. The easiest way might be to introduce PREEMPT_DYNAMIC that depends/selects PREEMPT. That way you're basically running a PREEMPT=y kernel. Then have PREEMPT_DYNAMIC allow disabling the __preempt_schedule / preempt_schedule_irq() callsites using static_call/static_branch respectively. That is, work backwards (from PREEMPT back to VOLUNTARY) instead of the other way around.