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=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS 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 B76FDC43381 for ; Mon, 25 Mar 2019 09:56:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7EA7E20870 for ; Mon, 25 Mar 2019 09:56:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1553507815; bh=RahqOi3+qNpPYHNCn8iuJpEvxWxzXDyhr6DYSRbtG00=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=U7Npr9GvqVOeNK6spQ5PjKnxAXE+KznGyVap0PJz3RgrssIv50ozFvIffzPyue0aS Kfb2ESEY0Lv3RFdTyUS/fQ8P/Qfz97r+6RS1LUFbUD74cpIWvBa05zrkSg54AcB3cc 1envLHYEB2EoXR1lYWEUFqm5mYyFs57vmF7htDn0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730409AbfCYJ4y (ORCPT ); Mon, 25 Mar 2019 05:56:54 -0400 Received: from mail-oi1-f196.google.com ([209.85.167.196]:42446 "EHLO mail-oi1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730216AbfCYJ4x (ORCPT ); Mon, 25 Mar 2019 05:56:53 -0400 Received: by mail-oi1-f196.google.com with SMTP id w139so6425159oie.9; Mon, 25 Mar 2019 02:56:53 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=XOd9IT2dezh2M2cUgQ4aKfbEw2w2NXDJPkRGJfYzM+s=; b=ncLLxsX44EXmI2LNJA2TTu5bow9U4sg3SLFm6mHb9qCF8O+GK5NX78OoOoHILT2c4J gimDVY5MgodzO4A/Ay4A7Lwh8LvUOM7sjPgucw9ti30qwoGA01TRKRiKdqucFqlGRd80 MyRxjhhAbT2KIuWX7wizrElE86AkAu0JkYZdoBjujqYqOw0kzgE4YibByVzQ/4VuJb+L W9/GojV5Gcr2ZPcx7Z5Py/s6mDmFktCAhIyBTi52RSX8v+rk94gz+S4RJb5xg5Liieo4 sW6gKq92ZGlf3tkOlNdAsVBZJiZk7wNIKLPOaXoP84NBl00lgzcLBN9Ddi6RnQXDTnjY BxkQ== X-Gm-Message-State: APjAAAUqvyYc4BPE2hpEaP4xrdHSh8FeGl0PerjYXBEZZlqNh0ItSLJf hXFnU4d55Sbqgs44bzfWxMwG35K4KLMyABfkITY= X-Google-Smtp-Source: APXvYqz5hglFUb/WifAFET7+2tDLNrfyl0ZlxnGgoVLUrU+pq1McKD/0L77uPT/Xwa6AP3t3M2NbnWPjBqe1LCTDn4g= X-Received: by 2002:aca:8d3:: with SMTP id 202mr11171314oii.76.1553507813031; Mon, 25 Mar 2019 02:56:53 -0700 (PDT) MIME-Version: 1.0 References: <1637073.gl2OfxWTjI@aspire.rjw.lan> <1762575.ER2xjzr9E1@aspire.rjw.lan> <20190322150009.GY6058@hirez.programming.kicks-ass.net> In-Reply-To: <20190322150009.GY6058@hirez.programming.kicks-ass.net> From: "Rafael J. Wysocki" Date: Mon, 25 Mar 2019 10:56:42 +0100 Message-ID: Subject: Re: [PATCH 2/2] PM / arch: x86: MSR_IA32_ENERGY_PERF_BIAS sysfs interface To: Peter Zijlstra Cc: "Rafael J. Wysocki" , x86 , LKML , Len Brown , Linux PM , Srinivas Pandruvada , Laura Abbott , Thomas Gleixner , Ingo Molnar , Simon Schricker , Borislav Petkov , Hannes Reinecke Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 22, 2019 at 4:00 PM Peter Zijlstra wrote: > > On Thu, Mar 21, 2019 at 11:20:17PM +0100, Rafael J. Wysocki wrote: > > + ret = rdmsrl_on_cpu(cpu, MSR_IA32_ENERGY_PERF_BIAS, &epb); > > + if (ret < 0) > > + return ret; > > + > > + ret = wrmsrl_on_cpu(cpu, MSR_IA32_ENERGY_PERF_BIAS, > > + (epb & ~EPB_MASK) | val); > > That's two back-to-back IPIs and a giant waste. Giant with respect to what? I know that the read can be avoidable if more MSR bits are stored in memory, but I don't expect this i/f to be used very often (once per boot maybe or on AC<->DC changes at most), so I didn't think that this would be a good tradeoff. > If you'd use a proper msr shadow variable, you'd not have to do the > rdmsr_on_cpu :-) Not really. The MSR can be updated from elsewhere which is not controlled by this code.