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=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 BED5FFC6182 for ; Fri, 14 Sep 2018 08:51:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 80B0F20882 for ; Fri, 14 Sep 2018 08:51:23 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 80B0F20882 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com 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 S1728173AbeINOEv (ORCPT ); Fri, 14 Sep 2018 10:04:51 -0400 Received: from foss.arm.com ([217.140.101.70]:58430 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726618AbeINOEu (ORCPT ); Fri, 14 Sep 2018 10:04:50 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D7D1D18A; Fri, 14 Sep 2018 01:51:20 -0700 (PDT) Received: from e110439-lin (e110439-lin.emea.arm.com [10.4.12.126]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 149AC3F703; Fri, 14 Sep 2018 01:51:17 -0700 (PDT) Date: Fri, 14 Sep 2018 09:51:15 +0100 From: Patrick Bellasi To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Ingo Molnar , Tejun Heo , "Rafael J . Wysocki" , Viresh Kumar , Vincent Guittot , Paul Turner , Quentin Perret , Dietmar Eggemann , Morten Rasmussen , Juri Lelli , Todd Kjos , Joel Fernandes , Steve Muckle , Suren Baghdasaryan Subject: Re: [PATCH v4 02/16] sched/core: uclamp: map TASK's clamp values into CPU's clamp groups Message-ID: <20180914085115.GM1413@e110439-lin> References: <20180828135324.21976-1-patrick.bellasi@arm.com> <20180828135324.21976-3-patrick.bellasi@arm.com> <20180912134945.GZ24106@hirez.programming.kicks-ass.net> <20180912155619.GG1413@e110439-lin> <20180912161218.GW24082@hirez.programming.kicks-ass.net> <20180912173515.GH1413@e110439-lin> <20180912174236.GB24106@hirez.programming.kicks-ass.net> <20180912175202.GK1413@e110439-lin> <20180913191422.GZ24082@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180913191422.GZ24082@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 13-Sep 21:14, Peter Zijlstra wrote: > On Wed, Sep 12, 2018 at 06:52:02PM +0100, Patrick Bellasi wrote: > > On 12-Sep 19:42, Peter Zijlstra wrote: > > > On Wed, Sep 12, 2018 at 06:35:15PM +0100, Patrick Bellasi wrote: > > > > On 12-Sep 18:12, Peter Zijlstra wrote: > > > > > > > > No idea; but if you want to go all fancy you can replace he whole > > > > > uclamp_map thing with something like: > > > > > > > > > > struct uclamp_map { > > > > > union { > > > > > struct { > > > > > unsigned long v : 10; > > > > > unsigned long c : BITS_PER_LONG - 10; > > > > > }; > > > > > atomic_long_t s; > > > > > }; > > > > > }; > > > > > > > > That sounds really cool and scary at the same time :) > > > > > > > > The v:10 requires that we never set SCHED_CAPACITY_SCALE>1024 > > > > or that we use it to track a percentage value (i.e. [0..100]). > > > > > > Or we pick 11 bits, it seems unlikely that capacity be larger than 2k. > > > > Just remembered a past experience where we had unaligned access traps > > on some machine because... don't you see any potentially issue on > > using bitfleds like you suggest above ? > > > > I'm thinking to: > > > > commit 317d359df95d ("sched/core: Force proper alignment of 'struct util_est'") > > There should not be (and I'm still confused by that particular commit > you reference). If we access everything through the uclamp_map::s, and > only use the bitfields to interpret the results, it all 'works'. Yes, the problem above was different... still I was wondering if there could be bitfields related alignment issue lurking somewhere. But, as you say, if we always R/W atomically via uclamp_map::s there should be none. > The tricky thing we did earlier was trying to use u64 accesses for 2 > u32 variables. And somehow ia64 didn't get the alignment right. Right, np... sorry for the noise. -- #include Patrick Bellasi