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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 07EAAC0044C for ; Wed, 7 Nov 2018 14:14:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BA36220827 for ; Wed, 7 Nov 2018 14:14:28 +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="WxgBZtDg" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BA36220827 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730570AbeKGXo7 (ORCPT ); Wed, 7 Nov 2018 18:44:59 -0500 Received: from merlin.infradead.org ([205.233.59.134]:32934 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726830AbeKGXo7 (ORCPT ); Wed, 7 Nov 2018 18:44:59 -0500 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=SBcT9EGd6MxKrVHTreVJ4OinKK8AXjwR0pe7meQhuE8=; b=WxgBZtDgtqmmZYWiF2h+YmOpV bbzpQvZo5ky7JOz7keqgAeiKFrOlvp0HYHgwtLbrMCi/qCZTAslTudJOVTJ5diTRHUSGhtA9FOEci Od5wwjpfKzj478DSGVVzmqlCCCztqhJwPNmvVv9Ygg6ziZKxZVECDSqcny3baYgFgLip0HEEIoOYv KqMgXE2MZVqXLYU8ku1h8rj7+a8ia6ZgyvVRmdOWugLjljWvJwtAuNt+VCD/JPlCxP6TWETzOlaGW 3S+6dbvYK2aHw2Rmf/joxvxzW5kb42PFcW5+YHQTu7O5ZoCWdJm5GrgVlJ7x/15OwR3olhseiapLw E7AfADedQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1gKOb2-0006F5-PR; Wed, 07 Nov 2018 14:14:17 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 7A4C020284F98; Wed, 7 Nov 2018 15:14:14 +0100 (CET) Date: Wed, 7 Nov 2018 15:14:14 +0100 From: Peter Zijlstra To: Patrick Bellasi Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Ingo Molnar , Tejun Heo , "Rafael J . Wysocki" , Vincent Guittot , Viresh Kumar , Paul Turner , Quentin Perret , Dietmar Eggemann , Morten Rasmussen , Juri Lelli , Todd Kjos , Joel Fernandes , Steve Muckle , Suren Baghdasaryan Subject: Re: [PATCH v5 03/15] sched/core: uclamp: map TASK's clamp values into CPU's clamp groups Message-ID: <20181107141414.GF9761@hirez.programming.kicks-ass.net> References: <20181029183311.29175-1-patrick.bellasi@arm.com> <20181029183311.29175-4-patrick.bellasi@arm.com> <20181107131632.GP9781@hirez.programming.kicks-ass.net> <20181107135738.GE14309@e110439-lin> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181107135738.GE14309@e110439-lin> 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, Nov 07, 2018 at 01:57:38PM +0000, Patrick Bellasi wrote: > On 07-Nov 14:16, Peter Zijlstra wrote: > > Please write cmpxchg loops in the form: > > > > atomic_long_t *ptr = &uclamp_maps[clamp_id][group_id].adata; > > union uclamp_map old, new; > > > > old.data = atomic_long_read(ptr); > > do { > > new.data = old.data; > > new.se_cound--; > > } while (!atomic_long_try_cmpxchg(ptr, &old.data, new.data)); > > > > > > (same for all the others of course) > > Ok, I did that to save some indentation, but actually it's most > commonly used in a while loop... will update in v6. > > Out of curiosity, apart from code consistency, is that required also > specifically for any possible compiler related (mis)behavior ? No; it is just the 'normal' form my brain likes :-) And the try_cmpxchg() thing is slightly more efficient on x86 vs the traditional form: while (cmpxchg(ptr, old, new) != old)