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=-0.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED 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 45E08C43334 for ; Wed, 5 Sep 2018 09:11:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CC26E206BA for ; Wed, 5 Sep 2018 09:11:49 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=linaro.org header.i=@linaro.org header.b="Xq1DyZ6q" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CC26E206BA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linaro.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 S1727965AbeIENlD (ORCPT ); Wed, 5 Sep 2018 09:41:03 -0400 Received: from mail-io0-f177.google.com ([209.85.223.177]:36635 "EHLO mail-io0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726272AbeIENlC (ORCPT ); Wed, 5 Sep 2018 09:41:02 -0400 Received: by mail-io0-f177.google.com with SMTP id q5-v6so5386881iop.3 for ; Wed, 05 Sep 2018 02:11:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=1ODv8hk1dFKeFgmpydpsBgEkNER0NAuijChGnsK5t8U=; b=Xq1DyZ6qXF0N/sHoXyXzUj2WtRRQkxwmmD5BC4RS31XwmTc+JAe6YIk3CTOVNLfaG7 63RqdsYjPa7OcPLR9FnxeyMCF6ih0g86lvcnqWmBpHqDFk8rcSAsCkxvj1zqf3ufDobE Rpy7PfssBGgVmCA6JzzLhRR2fjadlxPzLzmfg= 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=1ODv8hk1dFKeFgmpydpsBgEkNER0NAuijChGnsK5t8U=; b=Y3QRCOPz73t3np+T34qtcZLVMR4I3FV7Q63BtyoqgM7LbPb0hG1lApaJAobA2xMCNA XGWlCN/InXIwok6WAtQu6YOvNfYL7lujoGN1sRV9Y5fRUno8m3KuptifzbKkHkBvuYzM xqafXzkwrYRI8ikApndVLM8mgLSmsNjBXmkrNhJrCB5/wC9KWsHG51TrihhFYiVDS2dP y+TMmOyq2qzS6Spz7++5U0b+hv39pmPg2kAhDRBWogaCvq7n4F3F2s2UkNmUljVeU8/+ FYCdrtjRc8P8ZY8ouIwBb/1ogUR4BAmX7a2yiiF54qHE64yPUFbHp2QLl5Dw2vmjKybE GoIA== X-Gm-Message-State: APzg51BXH/s9c2zhXiP63ZExmsb4neuFIhzXY6RAuICI5PcRPdlSj33q bz8x6KRKY6Qb0paGG0hfqflPof2t1TsGaQLNAizF8++Q X-Google-Smtp-Source: ANB0VdYdgsnnMEqRocx0r9preJsVUfPxR7M9oPW7IURWGy2bZHqygTqAGaPuZyl0CH3tOO3zcgb0fYvbfUi3mDP2Qrg= X-Received: by 2002:a6b:e51a:: with SMTP id y26-v6mr24069728ioc.42.1536138706476; Wed, 05 Sep 2018 02:11:46 -0700 (PDT) MIME-Version: 1.0 References: <1535548752-4434-1-git-send-email-vincent.guittot@linaro.org> <1535548752-4434-4-git-send-email-vincent.guittot@linaro.org> <20180904082424.GA2090@linux.vnet.ibm.com> <20180904093626.GA23936@linaro.org> <20180904103742.GC61288@linux.vnet.ibm.com> <20180905085029.GA57420@linux.vnet.ibm.com> In-Reply-To: <20180905085029.GA57420@linux.vnet.ibm.com> From: Vincent Guittot Date: Wed, 5 Sep 2018 11:11:35 +0200 Message-ID: Subject: Re: [RFC PATCH 3/4] sched/topology: remove smt_gain To: Srikar Dronamraju Cc: Peter Zijlstra , Ingo Molnar , linux-kernel 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 Wed, 5 Sep 2018 at 10:50, Srikar Dronamraju wrote: > > * Vincent Guittot [2018-09-05 09:36:42]: > > > > > > > I dont know of any systems that have come with single threaded and > > > multithreaded. However some user can still offline few threads in a core > > > while leaving other cores untouched. I dont really know why somebody > > > would want to do it. For example, some customer was toying with SMT 3 > > > mode in a SMT 8 power8 box. > > > > In this case, it means that we have the same core capacity whatever > > the number of CPUs > > and a core with SMT 3 will be set with the same compute capacity as > > the core with SMT 8. > > Does it still make sense ? > > > > To me it make sense atleast from a power 8 perspective, because SMT 1 > > SMT 2 > SMT 4 > SMT8. So if one core is configured for SMT 2 and other > core is configured for SMT4; all threads being busy, the individual > threads running on SMT2 core will complete more work than SMT 4 core > threads. I agree for individual thread capacity but at core group level, the core SMT 1 will have the same capacity as core group SMT 8 so load balance will try to balance evenly the tasks between the 2 cores whereas core SMT 8 > core SMT1 , isn't it ? > > -- > Thanks and Regards > Srikar Dronamraju >