From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on archive.lwn.net X-Spam-Level: X-Spam-Status: No, score=-5.7 required=5.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,RCVD_IN_DNSWL_HI autolearn=ham autolearn_force=no version=3.4.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by archive.lwn.net (Postfix) with ESMTP id 7649F7D089 for ; Wed, 12 Dec 2018 09:46:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726697AbeLLJqV (ORCPT ); Wed, 12 Dec 2018 04:46:21 -0500 Received: from merlin.infradead.org ([205.233.59.134]:56498 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726651AbeLLJqU (ORCPT ); Wed, 12 Dec 2018 04:46:20 -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=s/qc4uW6NBXupLnXJsYLmAJxT6wemoTcD/fG8c6HBDk=; b=YHlZvmttLn0SZ+bTZfk18C8Us nF/7C2fZhSrm+8PAjR1HnnY+qwCFohUlwSSiEhQY163EtRfRABTac2c+oIf710ObiC8SmDD1yyDIW DBaWmfZp0/G285HU560qki4wSbIYKBY6jwd7JiJJ9Z+Gdzq/CSFodKdRBTweGZe/NTEiLhtnbC08s Fz5jVYvldVCvw/vQCrQ4uzvS0s/K6wX0goFF3WfqBFkjYnVKMY2Tsd+f+Pu7TRBiZN13yLUcjZ1mg 3kzpmxhZK4xiKTtsr7Cb7MNETvFJdx0DJd2xAHiUJ/OvfU8TiL04Iw7kB7WtcreZUc+Xg2roJXlFZ ygJSTABGg==; 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 1gX15n-0006mR-Lm; Wed, 12 Dec 2018 09:46:11 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 360082075BF39; Wed, 12 Dec 2018 10:46:10 +0100 (CET) Date: Wed, 12 Dec 2018 10:46:10 +0100 From: Peter Zijlstra To: "Rafael J. Wysocki" Cc: "Rafael J. Wysocki" , Linux PM , Doug Smythies , Linux Kernel Mailing List , "open list:DOCUMENTATION" , Daniel Lezcano , Giovanni Gherdovich , Lorenzo Pieralisi Subject: Re: [PATCH v2] cpuidle: Add 'above' and 'below' idle state metrics Message-ID: <20181212094610.GW5289@hirez.programming.kicks-ass.net> References: <3514439.dzOWKx1Cjx@aspire.rjw.lan> <20181210122104.GL5289@hirez.programming.kicks-ass.net> <20181210225134.GB24811@worktop.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-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Tue, Dec 11, 2018 at 10:51:48AM +0100, Rafael J. Wysocki wrote: > On Mon, Dec 10, 2018 at 11:51 PM Peter Zijlstra wrote: > > Dunno; it could be cold cachelines, at which point it can be fairly > > expensive. Also, being stuck with API is fairly horrible if you want to > > 'fix' it. > > All of the cache lines involved should've been touched earlier in this > code path by the governor. At least menu and the new one both touch > them. > > The API part I'm not too worried about. I know it is useful and two > other people have told that to me already. :-) Like said on IRC; I mostly wanted to raise the issue of overhead due to stats and ABI -- it's something I've been bitten by too many times :/ If you're confident you're hitting the same lines with the already extant accouning (time and usage) and you cannot make the whole lot conditional because of ABI (bah) then I'll not stand in the way here. I agree the numbers are useful, I'm just weary of overhead.