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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 C8CF0C3A5A7 for ; Wed, 4 Sep 2019 15:53:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9DCAC22CED for ; Wed, 4 Sep 2019 15:53:03 +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="Ytr3Kn9f" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731447AbfIDPxC (ORCPT ); Wed, 4 Sep 2019 11:53:02 -0400 Received: from merlin.infradead.org ([205.233.59.134]:35840 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730277AbfIDPxC (ORCPT ); Wed, 4 Sep 2019 11:53:02 -0400 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: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=8TDR/c+lAQCA6VzFgOc66YwWj1UooKlQYcDecK0A9vs=; b=Ytr3Kn9fyUxNRw1W4bEBoF4oR 5EDayrOSS3bOKASvQq+H8bguHpglNFb6LSOccRrq963PygUUb91gdd+41PqWONWXxopWueVUT4MiA Ew4ow2y7RnSyHx7PIT38IDFipl/WhBj87VKr2TX7v46l2JsGR27nAek+gZ/JzMqaSoMl9FwGwuzj3 QihvI3sUf3QvprAlcyL3Ql7bHkyTz/uej7RiBknu5EzsiTCQNOsm84y7TBzqODWvL1B7GqABotU4s O13JV8Hts0FZi1XR+Qsz0Du/SF8lLTxeZDwyx2GJvJJYqlS/Dgp3/cKM9tcmIedksr30Vg4gwte1R fvmsx/vKQ==; 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 (Red Hat Linux)) id 1i5XaE-0007eX-Kk; Wed, 04 Sep 2019 15:52:34 +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 D24A83011DF; Wed, 4 Sep 2019 17:51:52 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 63F2F29D8ACE7; Wed, 4 Sep 2019 17:52:29 +0200 (CEST) Date: Wed, 4 Sep 2019 17:52:29 +0200 From: Peter Zijlstra To: Joel Fernandes Cc: Steven Rostedt , Alessio Balsini , mingo@kernel.org, juri.lelli@redhat.com, linux-kernel@vger.kernel.org, dietmar.eggemann@arm.com, luca.abeni@santannapisa.it, bristot@redhat.com, dvyukov@google.com, tglx@linutronix.de, vpillai@digitalocean.com, kernel-team@android.com, will.deacon@arm.com Subject: Re: [RFC][PATCH 01/13] sched/deadline: Impose global limits on sched_attr::sched_period Message-ID: <20190904155229.GT2332@hirez.programming.kicks-ass.net> References: <20190726161357.397880775@infradead.org> <20190802172104.GA134279@google.com> <20190805115309.GJ2349@hirez.programming.kicks-ass.net> <20190822122949.GA245353@google.com> <20190822165125.GW2369@hirez.programming.kicks-ass.net> <20190831144117.GA133727@google.com> <20190902091623.GQ2349@hirez.programming.kicks-ass.net> <20190904061616.25ce79e1@oasis.local.home> <20190904113038.GE2349@hirez.programming.kicks-ass.net> <20190904132418.GA237277@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190904132418.GA237277@google.com> 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 Wed, Sep 04, 2019 at 09:24:18AM -0400, Joel Fernandes wrote: > On Wed, Sep 04, 2019 at 01:30:38PM +0200, Peter Zijlstra wrote: > > On Wed, Sep 04, 2019 at 06:16:16AM -0400, Steven Rostedt wrote: > > > On Mon, 2 Sep 2019 11:16:23 +0200 > > > Peter Zijlstra wrote: > > > > > > > in sched_dl_period_handler(). And do: > > > > > > > > + preempt_disable(); > > > > max = (u64)READ_ONCE(sysctl_sched_dl_period_max) * NSEC_PER_USEC; > > > > min = (u64)READ_ONCE(sysctl_sched_dl_period_min) * NSEC_PER_USEC; > > > > + preempt_enable(); > > > > > > Hmm, I'm curious. Doesn't the preempt_disable/enable() also add > > > compiler barriers which would remove the need for the READ_ONCE()s here? > > > > They do add compiler barriers; but they do not avoid the compiler > > tearing stuff up. > > Neither does WRITE_ONCE() on some possibly buggy but currently circulating > compilers :( Yes, I'm aware :/