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=-5.8 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 CF73CC388F9 for ; Fri, 20 Nov 2020 01:34:05 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 5D30D22259 for ; Fri, 20 Nov 2020 01:34:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="NAMeNEti"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="GqiCV9WE" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5D30D22259 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linutronix.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id DF6616B0074; Thu, 19 Nov 2020 20:34:02 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id DA72F6B0075; Thu, 19 Nov 2020 20:34:02 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CE3F26B007B; Thu, 19 Nov 2020 20:34:02 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0046.hostedemail.com [216.40.44.46]) by kanga.kvack.org (Postfix) with ESMTP id 965776B0074 for ; Thu, 19 Nov 2020 20:34:02 -0500 (EST) Received: from smtpin21.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 2E71C181AEF0B for ; Fri, 20 Nov 2020 01:34:02 +0000 (UTC) X-FDA: 77503075524.21.look60_050cfa127347 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin21.hostedemail.com (Postfix) with ESMTP id 10274180458E1 for ; Fri, 20 Nov 2020 01:34:02 +0000 (UTC) X-HE-Tag: look60_050cfa127347 X-Filterd-Recvd-Size: 4493 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by imf30.hostedemail.com (Postfix) with ESMTP for ; Fri, 20 Nov 2020 01:34:01 +0000 (UTC) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1605836039; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=7uVXnrJ9FAHgnGZVOERteDJIBOwguyPNBYIyccpfRao=; b=NAMeNEtibzZCn6hDuW13u0nNgnZbAGdYUadbXSfXJ0ejcSxinYzIKbQY/P1IpwrIxSolDO rb4gtDfC8Nx3wegNgQB5xyMdEvSkspebzNdd97Le/YpAHCp0SWi8dabyZF4rAF7ZZ0NjMz d2rJavDGJXKOvkXAKlnCXcWNr7X/30XYlMoTrOke4uXSm4H44kZUnxyq4/hWt9TFMSMhds I2RF7TdU2VsWyuKaVpcRuiC+qkMFKVYJ7I6jfokGa5zhPRDBHRHw3JyFrme4C9toAt9cg3 qO8V23fljRGzJxr3gtn1NzOwABh2wV9nk6e0J+8D5/lpGH4JIW/L1poK/YdalA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1605836039; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=7uVXnrJ9FAHgnGZVOERteDJIBOwguyPNBYIyccpfRao=; b=GqiCV9WE4RMEEngiPAHJwiWdyRGOC53LmO3t4JbfwinMQGX7dhTJffqL6hU3+HseoFu0jo ooj9V8+xI59X2HCQ== To: Peter Zijlstra , Linus Torvalds Cc: Mel Gorman , LKML , the arch/x86 maintainers , Christoph Hellwig , Matthew Wilcox , Daniel Vetter , Andrew Morton , Linux-MM , Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Daniel Bristot de Oliveira Subject: Re: [patch V4 4/8] sched: Make migrate_disable/enable() independent of RT In-Reply-To: <20201119182843.GA2414@hirez.programming.kicks-ass.net> References: <20201118194838.753436396@linutronix.de> <20201118204007.269943012@linutronix.de> <20201119093834.GH3306@suse.de> <20201119111411.GL3121378@hirez.programming.kicks-ass.net> <20201119182843.GA2414@hirez.programming.kicks-ass.net> Date: Fri, 20 Nov 2020 02:33:58 +0100 Message-ID: <87tutkolq1.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Nov 19 2020 at 19:28, Peter Zijlstra wrote: > On Thu, Nov 19, 2020 at 09:23:47AM -0800, Linus Torvalds wrote: >> Because this is certainly not the only time migration limiting has >> come up, and no, it has absolutely nothing to do with per-cpu page >> tables being completely unacceptable. > > It is for this instance; but sure, it's come up before in other > contexts. Indeed. And one of the really bad outcomes of this is that people are forced to use preempt_disable() to prevent migration which entails a slew of consequences: - Using spinlocks where it wouldn't be needed otherwise - Spinwaiting instead of sleeping - The whole crazyness of doing copy_to/from_user_in_atomic() along with the necessary out of line error handling. - .... The introduction of per-cpu storage happened almost 20 years ago (2002) and still the only answer we have is preempt_disable(). I know the scheduling theory folks still try to wrap their heads around the introduction of SMP which dates back to 1962 IIRC... >> The scheduler people need to get used to this. Really. Because ASMP is >> just going to be a fact. > > ASMP is different in that it is a hardware constraint, you're just not > going to be able to run more of X than there's X capable hardware units > on (be if FPUs, Vector units, 32bit or whatever) ASMP is as old as SMP. The first SMP systems were in fact ASMP. The reasons for ASMP 60 years ago were not that different from the reasons for ASMP today. Just the scale and the effectivness are different. >> There are few things more futile than railing against reality, Peter. > > But, but, my windmills! :-) At least you have windmills where you live so you can pull off the real Don Quixote while other people have to find substitutes :) Thanks, tglx