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 049EEC43334 for ; Thu, 6 Sep 2018 09:21:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9AF4F206BA for ; Thu, 6 Sep 2018 09:21:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=linaro.org header.i=@linaro.org header.b="LTzghy+Z" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9AF4F206BA 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 S1728399AbeIFN4N (ORCPT ); Thu, 6 Sep 2018 09:56:13 -0400 Received: from mail-it0-f52.google.com ([209.85.214.52]:39744 "EHLO mail-it0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728024AbeIFN4N (ORCPT ); Thu, 6 Sep 2018 09:56:13 -0400 Received: by mail-it0-f52.google.com with SMTP id h1-v6so13250925itj.4 for ; Thu, 06 Sep 2018 02:21:40 -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=eAC5g786jXAzkgPDVOMEFKwLTdpe+IQiz/vV9rnVBnU=; b=LTzghy+ZqwMb65NTjATFP27YnAES8tuKd3Hi1ATAxQ+H8ZecH8Wwt/K+dfjMzJN2jV dSW/VOSpICB4qzSDoOXnWHUGbOKtR7EbSv9hkzeWnP9NcP7+RVVUhanfiWauzd61nkYi j/1+y7ZHiEM65Od9m5BHbTNuOXT3nU3zzWiMs= 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=eAC5g786jXAzkgPDVOMEFKwLTdpe+IQiz/vV9rnVBnU=; b=AtBuWX6dzcloWTNR4gjpW7zJ7LJ8mBKdV91hBDsNmFgudyot7zpJMTrIU8KiyOfHde Nj/qqEkx9TagyGjjrxcSvCDDU7mS4BOshj+4iBm8NJ3/U67K7zTQUIjT+pgKygESu7A8 +hBqbWPPT/bWSZHH/JUKYzBxp6gCSSMrsPETu0UF8eskpJefMF5pNvCgk8SmZBE6zsjz qyNd/cEw/Pw5//DAixbVEksrHOZOBvW42hLEKqaJyS9P3b8Hx2e9EeLmgFNqxwomlRJb IctErb6aOfiWuwQXRQ3O9oOAP06JlsgBhHFPfFt5ttFfvu7KUqq+S764T/5nzqhHfHev TmHg== X-Gm-Message-State: APzg51CDmAttnPocqsb4pHz9Ltrl+mbH0YLbIqTYB8eWTC02BGKN5t/j vZgXpSNUgwInQCw0knve/bst0CKZHs0Fd1AJMmSe7Q== X-Google-Smtp-Source: ANB0VdYJJqlyqt++X2kWiI3B/1tKTwRwpdQ0OoFkN0hdFRqcM74qUoRrjEPhz+wlEDQm9/ymBNX/BzQ/V47rII+VGJY= X-Received: by 2002:a24:e00e:: with SMTP id c14-v6mr1908430ith.108.1536225700132; Thu, 06 Sep 2018 02:21:40 -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> <20180905111436.GB57420@linux.vnet.ibm.com> In-Reply-To: <20180905111436.GB57420@linux.vnet.ibm.com> From: Vincent Guittot Date: Thu, 6 Sep 2018 11:21:29 +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 13:14, Srikar Dronamraju wrote: > > * Vincent Guittot [2018-09-05 11:11:35]: > > > 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 ? > > > > I believe that Core capacity irrespective of the number of threads > should be similar. We wanted to give a small benefit if the core has > multiple threads and that was smt_gain. Lets say we have 8 equal sw > threads running on 2 cores; one being SMT 2 and other being SMT4. > then 4 threads should be spread to each core. So that we would be fair > to each of the 8 SW threads. Do you mean that it would be the same with SMT 2 and SMT 8 ? evenly spread the 8 SW threads between the 2 cores would be better than 2 SW threads on core SMT 2 and 6 on core SMT8 > > -- > Thanks and Regards > Srikar Dronamraju >