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[209.132.180.67]) by mx.google.com with ESMTP id f1-v6si7860575pld.49.2018.10.25.04.29.55; Thu, 25 Oct 2018 04:30:12 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=pass header.i=@oracle.com header.s=corp-2018-07-02 header.b="h/8+wxBW"; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=oracle.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727308AbeJYUB4 (ORCPT + 99 others); Thu, 25 Oct 2018 16:01:56 -0400 Received: from userp2130.oracle.com ([156.151.31.86]:53848 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727208AbeJYUB4 (ORCPT ); Thu, 25 Oct 2018 16:01:56 -0400 Received: from pps.filterd (userp2130.oracle.com [127.0.0.1]) by userp2130.oracle.com (8.16.0.22/8.16.0.22) with SMTP id w9PBT27r023065; Thu, 25 Oct 2018 11:29:10 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=subject : to : cc : references : from : message-id : date : mime-version : in-reply-to : content-type : content-transfer-encoding; s=corp-2018-07-02; bh=wMokk2O+zI/6oAUVJtLigYRBW3nS1rtC/oZhoh3PFLs=; b=h/8+wxBWWqDeYw4+dR5u+S4QBgOBihTf7x04W6oNNky3vckv91zHbIf9y93bgU7AJYpS U03r8V6XRG+JkEHLBAhjHeVHQrDt8an6z+o3z5csYiCumBsPtt2dU3VPFrHEZ/kOLfcN caDhXaMho6f/THQPXEmXPCl7Y6hgsKwkjpVf2rKBLzgp0ugt3vCziMYBzEeUVKpY751S dk0IfsYfyVfiv74FaPQ/kFp2hbnOo0oJCt0QiCRBejJmlVGglzPUFd2ZgVV/53so8+5q 3HYOu/JLAGYMww8o1HMmvrIt8yfxaRu9U/ZutD8N54doEN7ROToDcqPtSZcjvxGctlNM Wg== Received: from aserv0021.oracle.com (aserv0021.oracle.com [141.146.126.233]) by userp2130.oracle.com with ESMTP id 2n7usuh0r4-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 25 Oct 2018 11:29:09 +0000 Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by aserv0021.oracle.com (8.14.4/8.14.4) with ESMTP id w9PBT8CM012887 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 25 Oct 2018 11:29:09 GMT Received: from abhmp0008.oracle.com (abhmp0008.oracle.com [141.146.116.14]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id w9PBT7AM006004; Thu, 25 Oct 2018 11:29:07 GMT Received: from [10.152.35.100] (/10.152.35.100) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Thu, 25 Oct 2018 04:29:07 -0700 Subject: Re: [PATCH 00/10] steal tasks to improve CPU utilization To: Vincent Guittot Cc: Ingo Molnar , Peter Zijlstra , subhra.mazumdar@oracle.com, Dhaval Giani , Rohit Jain , daniel.m.jordan@oracle.com, pavel.tatashin@microsoft.com, Matt Fleming , Mike Galbraith , Rik van Riel , Josef Bacik , Juri Lelli , linux-kernel References: <1540220381-424433-1-git-send-email-steven.sistare@oracle.com> From: Steven Sistare Organization: Oracle Corporation Message-ID: <89a6c01e-c911-04ed-b434-9f93f90da66c@oracle.com> Date: Thu, 25 Oct 2018 07:28:49 -0400 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9056 signatures=668683 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1807170000 definitions=main-1810250103 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/25/2018 3:50 AM, Vincent Guittot wrote: > Hi Steve, > > On Mon, 22 Oct 2018 at 17:10, Steve Sistare wrote: >> >> When a CPU has no more CFS tasks to run, and idle_balance() fails to >> find a task, then attempt to steal a task from an overloaded CPU in the >> same LLC. Maintain and use a bitmap of overloaded CPUs to efficiently >> identify candidates. To minimize search time, steal the first migratable >> task that is found when the bitmap is traversed. For fairness, search >> for migratable tasks on an overloaded CPU in order of next to run. >> >> This simple stealing yields a higher CPU utilization than idle_balance() >> alone, because the search is cheap, so it may be called every time the CPU >> is about to go idle. idle_balance() does more work because it searches >> widely for the busiest queue, so to limit its CPU consumption, it declines >> to search if the system is too busy. Simple stealing does not offload the >> globally busiest queue, but it is much better than running nothing at all. >> >> The bitmap of overloaded CPUs is a new type of sparse bitmap, designed to >> reduce cache contention vs the usual bitmap when many threads concurrently >> set, clear, and visit elements. >> >> Patch 1 defines the sparsemask type and its operations. >> >> Patches 2, 3, and 4 implement the bitmap of overloaded CPUs. >> >> Patches 5 and 6 refactor existing code for a cleaner merge of later >> patches. >> >> Patches 7 and 8 implement task stealing using the overloaded CPUs bitmap. >> >> Patch 9 disables stealing on systems with more than 2 NUMA nodes for the >> time being because of performance regressions that are not due to stealing >> per-se. See the patch description for details. >> >> Patch 10 adds schedstats for comparing the new behavior to the old, and >> provided as a convenience for developers only, not for integration. >> >> The patch series is based on kernel 4.19.0-rc7. It compiles, boots, and >> runs with/without each of CONFIG_SCHED_SMT, CONFIG_SMP, CONFIG_SCHED_DEBUG, >> and CONFIG_PREEMPT. It runs without error with CONFIG_DEBUG_PREEMPT + >> CONFIG_SLUB_DEBUG + CONFIG_DEBUG_PAGEALLOC + CONFIG_DEBUG_MUTEXES + >> CONFIG_DEBUG_SPINLOCK + CONFIG_DEBUG_ATOMIC_SLEEP. CPU hot plug and CPU >> bandwidth control were tested. >> >> Stealing imprroves utilization with only a modest CPU overhead in scheduler >> code. In the following experiment, hackbench is run with varying numbers >> of groups (40 tasks per group), and the delta in /proc/schedstat is shown >> for each run, averaged per CPU, augmented with these non-standard stats: >> >> %find - percent of time spent in old and new functions that search for >> idle CPUs and tasks to steal and set the overloaded CPUs bitmap. >> >> steal - number of times a task is stolen from another CPU. >> >> X6-2: 1 socket * 10 cores * 2 hyperthreads = 20 CPUs >> Intel(R) Xeon(R) CPU E5-2630 v4 @ 2.20GHz >> hackbench process 100000 >> sched_wakeup_granularity_ns=15000000 > > Why do you mention this sched_wakeup_granularity_ns value ? > It is something that you changed for you tests ? > The comment for this tunable says that default value is 1ms * > ilog(ncpus) = 4ms for 20CPUs I changed it for the test, and I explain why a few paragraphs later. The value matches the one set by tuned.service, for those running it. - Steve > >> >> baseline >> grps time %busy slice sched idle wake %find steal >> 1 8.084 75.02 0.10 105476 46291 59183 0.31 0 >> 2 13.892 85.33 0.10 190225 70958 119264 0.45 0 >> 3 19.668 89.04 0.10 263896 87047 176850 0.49 0 >> 4 25.279 91.28 0.10 322171 94691 227474 0.51 0 >> 8 47.832 94.86 0.09 630636 144141 486322 0.56 0 >> >> new >> grps time %busy slice sched idle wake %find steal %speedup >> 1 5.938 96.80 0.24 31255 7190 24061 0.63 7433 36.1 >> 2 11.491 99.23 0.16 74097 4578 69512 0.84 19463 20.9 >> 3 16.987 99.66 0.15 115824 1985 113826 0.77 24707 15.8 >> 4 22.504 99.80 0.14 167188 2385 164786 0.75 29353 12.3 >> 8 44.441 99.86 0.11 389153 1616 387401 0.67 38190 7.6 >> >> Elapsed time improves by 8 to 36%, and CPU busy utilization is up >> by 5 to 22% hitting 99% for 2 or more groups (80 or more tasks). >> The cost is at most 0.4% more find time. > >>