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=-2.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 B97CEC3A5A2 for ; Tue, 3 Sep 2019 19:47:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 908F221881 for ; Tue, 3 Sep 2019 19:47:00 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="XXl2aHLE" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726965AbfICTq7 (ORCPT ); Tue, 3 Sep 2019 15:46:59 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:49840 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726179AbfICTq5 (ORCPT ); Tue, 3 Sep 2019 15:46:57 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=0oSK57qWeSItTDz/D1Y7sd4ufyamhAWf1L+/fFFqZyQ=; b=XXl2aHLEUe68XutV+fxkA3608 I7vNH9lR5XVbY+UgpzYTbkAox4OSJ03Bzgs3NwC0AtJMaQw1As2aLxpN8Opt30kA1U8WEKusrExp6 4fUj9HPZD+tR0VciCPG3qSl/CZARQgij/0mwWRcGQqaK3Q/H3iIfcz5rcG6VHDIG+iIP7zCdhLSWo VbE53FBHmuMfjWaaoQGBr9JeLAyEjQVpBOkVOpBWFHw+vEVA4HVG1vjbX5cV6Be3UooOVtF2p/cyz od9fmPPSm39VMMPVLf52xTnV3ErNBwd528mnkG76Q8EQ8wp6M4y0FiJ01d6F6zOLuhVe7If542Lb6 /Cvczd0Hg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1i5ElH-0000KZ-UH; Tue, 03 Sep 2019 19:46:44 +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 F1B33306010; Tue, 3 Sep 2019 21:46:05 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 3CE6B20977765; Tue, 3 Sep 2019 21:46:42 +0200 (CEST) Date: Tue, 3 Sep 2019 21:46:42 +0200 From: Peter Zijlstra To: Linus Torvalds Cc: "Eric W. Biederman" , "Paul E. McKenney" , Oleg Nesterov , Russell King - ARM Linux admin , Chris Metcalf , Christoph Lameter , Kirill Tkhai , Mike Galbraith , Thomas Gleixner , Ingo Molnar , Linux List Kernel Mailing , Davidlohr Bueso Subject: Re: [PATCH 0/3] task: Making tasks on the runqueue rcu protected Message-ID: <20190903194642.GV2349@hirez.programming.kicks-ass.net> References: <20190830160957.GC2634@redhat.com> <87o906wimo.fsf@x220.int.ebiederm.org> <20190902134003.GA14770@redhat.com> <87tv9uiq9r.fsf@x220.int.ebiederm.org> <87k1aqt23r.fsf_-_@x220.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 03, 2019 at 08:44:40AM -0700, Linus Torvalds wrote: > That said, it won't affect any of the core architectures much, because > smp_store_release() isn't that expensive (it's just a compiler barrier > on x86, it's a cheap instruction on arm64, and it should be very cheap > on any other architecture too unless they do insane things - even on > powerpc, which is about the worst case for any barriers, it's just an > lwsync). Right, x86/s390/Sparc it's a compiler barrier, ARM64 has a store-release op which is relatively cheap, Power has an LWSYNC, but the rest does store-release with smp_mb() -- and this includes ARM.