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 A026EC4360C for ; Tue, 8 Oct 2019 16:34:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7423920815 for ; Tue, 8 Oct 2019 16:34:07 +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="mRfIojx7" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729436AbfJHQeG (ORCPT ); Tue, 8 Oct 2019 12:34:06 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:55368 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727865AbfJHQeE (ORCPT ); Tue, 8 Oct 2019 12:34:04 -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=LxGaMkqOaVvBpkVPmUmLJlqT8yEBVyNhBC4qVA6fBh4=; b=mRfIojx7gWC8lLI7BRQ4v+LXs BZ7jrfy0PLhJVKY5bHgHqZXy43Cs4h1nYHSRutRBMouvnPwuF/G75FO+TbUqXeN4ZA3EgzWdUSw9q r7L1yCNSUqTmXVUkekaLLP08cnyVyLHzQx5KOZTcW2i2g2ISBMJEhvrp9kC//b3Mj1GeiDyuxFnJt l09GKlZUDk1Hk+/risdVcMcnDHIHtBZCNhLe6f1I/x8w94lMejQMc4J0Xp7UFEaW/iSIubxCghtr0 jNTtrzczk2mQNQT9FGfKAHMeuf7LEV+yGKtCAkerz7mEB35SWK39FGrJAB6TiWXjJehvZHYBXzQID WmeKFTBZg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92.2 #3 (Red Hat Linux)) id 1iHsQx-0000xV-Pe; Tue, 08 Oct 2019 16:33:59 +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 56D5A305E1D; Tue, 8 Oct 2019 18:33:06 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id BEC2420247CA6; Tue, 8 Oct 2019 18:33:57 +0200 (CEST) Date: Tue, 8 Oct 2019 18:33:57 +0200 From: Peter Zijlstra To: Valentin Schneider Cc: Vincent Guittot , linux-kernel , Ingo Molnar , Phil Auld , Srikar Dronamraju , Quentin Perret , Dietmar Eggemann , Morten Rasmussen , Hillf Danton Subject: Re: [PATCH v3 04/10] sched/fair: rework load_balance Message-ID: <20191008163357.GF2328@hirez.programming.kicks-ass.net> References: <1568878421-12301-1-git-send-email-vincent.guittot@linaro.org> <1568878421-12301-5-git-send-email-vincent.guittot@linaro.org> <31cac0c1-98e4-c70e-e156-51a70813beff@arm.com> <20191008141642.GQ2294@hirez.programming.kicks-ass.net> 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, Oct 08, 2019 at 03:34:04PM +0100, Valentin Schneider wrote: > On 08/10/2019 15:16, Peter Zijlstra wrote: > > On Wed, Oct 02, 2019 at 11:47:59AM +0100, Valentin Schneider wrote: > > > >> Yeah, right shift on signed negative values are implementation defined. > > > > Seriously? Even under -fno-strict-overflow? There is a perfectly > > sensible operation for signed shift right, this stuff should not be > > undefined. > > > > Mmm good point. I didn't see anything relevant in the description of that > flag. All my copy of the C99 standard (draft) says at 6.5.7.5 is: > > """ > The result of E1 >> E2 [...] If E1 has a signed type and a negative value, > the resulting value is implementation-defined. > """ > > Arithmetic shift would make sense, but I think this stems from twos' > complement not being imposed: 6.2.6.2.2 says sign can be done with > sign + magnitude, twos complement or ones' complement... But -fno-strict-overflow mandates 2s complement for all such signed issues.