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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 17EFFC4332B for ; Fri, 20 Mar 2020 15:34:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DDF832070A for ; Fri, 20 Mar 2020 15:34:00 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="SJySvP5t" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727460AbgCTPd7 (ORCPT ); Fri, 20 Mar 2020 11:33:59 -0400 Received: from us-smtp-delivery-74.mimecast.com ([63.128.21.74]:21563 "EHLO us-smtp-delivery-74.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726144AbgCTPd7 (ORCPT ); Fri, 20 Mar 2020 11:33:59 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1584718437; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=XeyzAJxgBh+6PUhoAp4SlYW+6ERsTWH0yvGznNw4e58=; b=SJySvP5t7Ke36aysK+gsB4vK3pgSuBO/EbFoP19BDAvXKO6GhkKFlY9maxOtR9NprJHbdx p9l+rFBvz1L/OxeSAUa5n7GXjmMIDLOYKV7ynQwkPuSOoj45x5ZOGrhru8MR7+sSwzF7AG IXDtQALCMlfFoDV9QSMQKISr4epyhlM= Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-256-xzBkP3V0NVGssPUd_ueYng-1; Fri, 20 Mar 2020 11:33:55 -0400 X-MC-Unique: xzBkP3V0NVGssPUd_ueYng-1 Received: by mail-wm1-f70.google.com with SMTP id f185so2503176wmf.8 for ; Fri, 20 Mar 2020 08:33:55 -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; bh=XeyzAJxgBh+6PUhoAp4SlYW+6ERsTWH0yvGznNw4e58=; b=r+rzIlWjacC5H0Dz1C8D8on2s5hE7pEajjrFCH9EDo7xk8uDXEEZRpaARAZoe8nLOr Oqvb/RXAMaQ/D1xMM9QcOpk2mfDLkosIJpNMy76Igww/Xw35TWvcYFc7uAJMX2LPO5sg Neez5P2Ahla0YxWunPDtmkjblJ1BT6BJ9CJpu97jrfxL8PyMknK9XFl3pwIn4RkzVlu9 u5ja1gwZeZxS//HwgL1pc1YXKYUIWv/y3h+Wck0iw3Mr6D72jYfrre5duMtvTzXIXwQM FMJ+D2yFMc9Q2BVuG9cUXI9qgqDg9LeYo8erkxl83NnuCSGzn4zcveaTeXmd6QyTFxgJ WsUA== X-Gm-Message-State: ANhLgQ1yqyaBCms4B9hM9TaYSqTaL0WNkDot2JaBaJ+kJfANriE2wsMn P6dIesebbWILKOstvqhkxXRlim8yQojqX7ZDQx3fwP5P8Dj4NTAUsb4i5aNoZSZOOcNrGveUB5m ZwsLHy9htE8ZFVH9B3tFAazwFRl4N64Y8hChD12eP X-Received: by 2002:a7b:c40f:: with SMTP id k15mr5696842wmi.144.1584718434412; Fri, 20 Mar 2020 08:33:54 -0700 (PDT) X-Google-Smtp-Source: ADFU+vuDBST3/7qZQPX/Zppz7rPxOCK13Gbo/YEvu+3q6wsOmXOKe/OICTow4GBaSf+RSlljQr+C0CfYFyEuy0h6EQw= X-Received: by 2002:a7b:c40f:: with SMTP id k15mr5696810wmi.144.1584718434072; Fri, 20 Mar 2020 08:33:54 -0700 (PDT) MIME-Version: 1.0 References: <20200224095223.13361-1-mgorman@techsingularity.net> <20200309191233.GG10065@pauld.bos.csb> <20200309203625.GU3818@techsingularity.net> <20200312095432.GW3818@techsingularity.net> <20200312155640.GX3818@techsingularity.net> <20200312214736.GA3818@techsingularity.net> <20200320152251.GC3818@techsingularity.net> In-Reply-To: <20200320152251.GC3818@techsingularity.net> From: Jirka Hladky Date: Fri, 20 Mar 2020 16:33:43 +0100 Message-ID: Subject: Re: [PATCH 00/13] Reconcile NUMA balancing decisions with the load balancer v6 To: 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 > MPI or OMP and what is a low thread count? For MPI at least, I saw a 0.4% > gain on an 4-node machine for bt_C and a 3.88% regression on 8-nodes. I > think it must be OMP you are using because I found I had to disable UA > for MPI at some point in the past for reasons I no longer remember. Yes, it's indeed OMP. With low threads count, I mean up to 2x number of NUMA nodes (8 threads on 4 NUMA node servers, 16 threads on 8 NUMA node servers). > One possibility would be to spread wide always at clone time and assume > wake_affine will pull related tasks but it's fragile because it breaks > if the cloned task execs and then allocates memory from a remote node > only to migrate to a local node immediately. I think the only way to find out how it performs is to test it. If you could prepare a patch like that, I'm more than happy to give it a try! Jirka On Fri, Mar 20, 2020 at 4:22 PM Mel Gorman wrote: > > On Fri, Mar 20, 2020 at 03:37:44PM +0100, Jirka Hladky wrote: > > Hi Mel, > > > > just a quick update. I have increased the testing coverage and other tests > > from the NAS shows a big performance drop for the low number of threads as > > well: > > > > sp_C_x - show still the biggest drop upto 50% > > bt_C_x - performance drop upto 40% > > ua_C_x - performance drop upto 30% > > > > MPI or OMP and what is a low thread count? For MPI at least, I saw a 0.4% > gain on an 4-node machine for bt_C and a 3.88% regression on 8-nodes. I > think it must be OMP you are using because I found I had to disable UA > for MPI at some point in the past for reasons I no longer remember. > > > My point is that the performance drop for the low number of threads is more > > common than we have initially thought. > > > > Let me know what you need more data. > > > > I just a clarification on the thread count and a confirmation it's OMP. For > MPI, I did note that some of the other NAS kernels shows a slight dip but > it was nowhere near as severe as SP and the problem was the same as more -- > two or more tasks stayed on the same node without spreading out because > there was no pressure to do so. There was enough CPU and memory capacity > with no obvious pattern that could be used to spread the load wide early. > > One possibility would be to spread wide always at clone time and assume > wake_affine will pull related tasks but it's fragile because it breaks > if the cloned task execs and then allocates memory from a remote node > only to migrate to a local node immediately. > > -- > Mel Gorman > SUSE Labs > -- -Jirka