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 5BD57C4332F for ; Wed, 8 Nov 2023 11:15:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344434AbjKHLP2 (ORCPT ); Wed, 8 Nov 2023 06:15:28 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49730 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229924AbjKHLPZ (ORCPT ); Wed, 8 Nov 2023 06:15:25 -0500 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5005919B3 for ; Wed, 8 Nov 2023 03:15:22 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; 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=LakYbXR3di9WRqWbciSUdlJrNzr3EZiBAXC/ZMZNW4g=; b=QGsg4EwJgCqNuGRPTI0kL4wSsi Y1tiUsZhpALUmcK71iy49kzBVviGpiZqeT0kugcoxjtWU0Wcftc8ra7EGyYo2qD8h72qMne2cej3/ hHUHjTdbWMGRFqtspUvAE7TNwbeb4RiN6r7al5zsDBjeEsZ1zMWDNCc6WDy3sfKtYC1lAa3mI97EQ 0iOHM1beg6B0bNmeiuc4Rax3Z0ynIt72v8dGIIXAx2Zp90FWRCpoFvBz8w6R/wZ1D0HeIDH9y9+GC vgtrpZSjuuWsXjWfB0yNjp8+hxyteRfgA129LsK6Ue/wIV0B6F4LdJ2SvKdZ8gcfS6IqKIrq9aPs/ SfeC7WPA==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.96 #2 (Red Hat Linux)) id 1r0gVj-00DR3j-2x; Wed, 08 Nov 2023 11:14:16 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 38A2B30049D; Wed, 8 Nov 2023 12:14:15 +0100 (CET) Date: Wed, 8 Nov 2023 12:14:15 +0100 From: Peter Zijlstra To: Ankur Arora Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, torvalds@linux-foundation.org, paulmck@kernel.org, linux-mm@kvack.org, x86@kernel.org, akpm@linux-foundation.org, luto@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, willy@infradead.org, mgorman@suse.de, jon.grimm@amd.com, bharata@amd.com, raghavendra.kt@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com, jgross@suse.com, andrew.cooper3@citrix.com, mingo@kernel.org, bristot@kernel.org, mathieu.desnoyers@efficios.com, geert@linux-m68k.org, glaubitz@physik.fu-berlin.de, anton.ivanov@cambridgegreys.com, mattst88@gmail.com, krypton@ulrich-teichert.org, rostedt@goodmis.org, David.Laight@aculab.com, richard@nod.at, mjguzik@gmail.com Subject: Re: [RFC PATCH 00/86] Make the kernel preemptible Message-ID: <20231108111415.GP8262@noisy.programming.kicks-ass.net> References: <20231107215742.363031-1-ankur.a.arora@oracle.com> <20231108085156.GD8262@noisy.programming.kicks-ass.net> <87bkc4lfxp.fsf@oracle.com> <20231108101330.GK3818@noisy.programming.kicks-ass.net> <87leb8ik6b.fsf@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87leb8ik6b.fsf@oracle.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 08, 2023 at 03:00:44AM -0800, Ankur Arora wrote: > Ah now I see what you are saying. > > Quick thought: even if we were running under NONE, eventually you'll Well, NONE, you get what you pay for etc.. > want to forcibly preempt out a CPU hog. So we will need to have > at least this one enabled always: > > > * irqentry_exit_cond_resched <- irqentry_exit_cond_resched > > These two, it might make sense to toggle them based on model. > > > * preempt_schedule <- preempt_schedule > > * preempt_schedule_notrace <- preempt_schedule_notrace > > Anyway let me think about this more and respond tomorrow. That's more or less killing NONE. At that point there's really no point in having it. I would really suggest you start with transforming VOLUNTARY into the LAZY thing, keep it as simple and narrow as possible. Once you've got that done, then you can try and argue that NONE makes no sense and try and take it out. Smaller step etc..