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=-4.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_PASS,UNPARSEABLE_RELAY,URIBL_BLOCKED,USER_AGENT_NEOMUTT 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 CE534C32789 for ; Tue, 6 Nov 2018 21:17:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8866720862 for ; Tue, 6 Nov 2018 21:17:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="pMVKyySm" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8866720862 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=oracle.com 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 S2388885AbeKGGoZ (ORCPT ); Wed, 7 Nov 2018 01:44:25 -0500 Received: from aserp2120.oracle.com ([141.146.126.78]:58602 "EHLO aserp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726918AbeKGGoX (ORCPT ); Wed, 7 Nov 2018 01:44:23 -0500 Received: from pps.filterd (aserp2120.oracle.com [127.0.0.1]) by aserp2120.oracle.com (8.16.0.22/8.16.0.22) with SMTP id wA6Is5t6188439; Tue, 6 Nov 2018 19:00:28 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=date : from : to : cc : subject : message-id : references : mime-version : content-type : in-reply-to; s=corp-2018-07-02; bh=KGb9NUxsKsh7FP4BpMAi0pNNtqYdI2Z+ZsN/Wb85+7Q=; b=pMVKyySmsDtN/sZdL8cn0t1yl0fj3ZYzR6R6ZBojPnG94TmcTHOydTmsVnBmcP+JhX0P VJYdWEVTBznBjAVBGZDrSUSkAUudhnmtNowGSnr6ALnZzkV1XdsFAoX9m/nTLCmcyBze HRI0rV95lh9BQUrBWdKoqbc0U0v6qDE5p5KnKzHUwndgiHJy4/OOm9iIl9svB1fSU8O2 YuCA+XfXDNgxpp1cBhCb1wY+Fz76PGjArq+zqm5mdWYeP88EktTZSN+kqGqFEoAmq+o+ mJVynwvf0LQ0XYrHNyNxrtstP3oH8wL4+RXuQCzDtj0eEGsCtGodQZXnEV415gk/Qc4Z Zg== Received: from userv0021.oracle.com (userv0021.oracle.com [156.151.31.71]) by aserp2120.oracle.com with ESMTP id 2nh3mpq7sk-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 06 Nov 2018 19:00:27 +0000 Received: from userv0122.oracle.com (userv0122.oracle.com [156.151.31.75]) by userv0021.oracle.com (8.14.4/8.14.4) with ESMTP id wA6J0RiV030496 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 6 Nov 2018 19:00:27 GMT Received: from abhmp0016.oracle.com (abhmp0016.oracle.com [141.146.116.22]) by userv0122.oracle.com (8.14.4/8.14.4) with ESMTP id wA6J0NNG008027; Tue, 6 Nov 2018 19:00:23 GMT Received: from ca-dmjordan1.us.oracle.com (/10.211.9.48) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 06 Nov 2018 11:00:22 -0800 Date: Tue, 6 Nov 2018 11:00:29 -0800 From: Daniel Jordan To: Zi Yan Cc: Daniel Jordan , linux-mm@kvack.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, aarcange@redhat.com, aaron.lu@intel.com, akpm@linux-foundation.org, alex.williamson@redhat.com, bsd@redhat.com, darrick.wong@oracle.com, dave.hansen@linux.intel.com, jgg@mellanox.com, jwadams@google.com, jiangshanlai@gmail.com, mhocko@kernel.org, mike.kravetz@oracle.com, Pavel.Tatashin@microsoft.com, prasad.singamsetty@oracle.com, rdunlap@infradead.org, steven.sistare@oracle.com, tim.c.chen@intel.com, tj@kernel.org, vbabka@suse.cz Subject: Re: [RFC PATCH v4 00/13] ktask: multithread CPU-intensive kernel work Message-ID: <20181106190029.epktpxhimrca4f4a@ca-dmjordan1.us.oracle.com> References: <20181105165558.11698-1-daniel.m.jordan@oracle.com> <20181106022024.ndn377ze6xljsxkb@ca-dmjordan1.us.oracle.com> <7E53DD63-4955-480D-8C0D-EB07E4FF011B@cs.rutgers.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7E53DD63-4955-480D-8C0D-EB07E4FF011B@cs.rutgers.edu> User-Agent: NeoMutt/20180323-268-5a959c X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9069 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-1811060164 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 05, 2018 at 09:48:56PM -0500, Zi Yan wrote: > On 5 Nov 2018, at 21:20, Daniel Jordan wrote: > > > Hi Zi, > > > > On Mon, Nov 05, 2018 at 01:49:14PM -0500, Zi Yan wrote: > >> On 5 Nov 2018, at 11:55, Daniel Jordan wrote: > >> > >> Do you think if it makes sense to use ktask for huge page migration (the data > >> copy part)? > > > > It certainly could. > > > >> I did some experiments back in 2016[1], which showed that migrating one 2MB page > >> with 8 threads could achieve 2.8x throughput of the existing single-threaded method. > >> The problem with my parallel page migration patchset at that time was that it > >> has no CPU-utilization awareness, which is solved by your patches now. > > > > Did you run with fewer than 8 threads? I'd want a bigger speedup than 2.8x for > > 8, and a smaller thread count might improve thread utilization. > > Yes. When migrating one 2MB THP with migrate_pages() system call on a two-socket server > with 2 E5-2650 v3 CPUs (10 cores per socket) across two sockets, here are the page migration > throughput numbers: > > throughput factor > 1 thread 2.15 GB/s 1x > 2 threads 3.05 GB/s 1.42x > 4 threads 4.50 GB/s 2.09x > 8 threads 5.98 GB/s 2.78x Thanks. Looks like in your patches you start a worker for every piece of the huge page copy and have the main thread wait. I'm curious what the workqueue overhead is like on your machine. On a newer Xeon it's ~50usec from queueing a work to starting to execute it and another ~20usec to flush a work (barrier_func), which could happen after the work is already done. A pretty significant piece of the copy time for part of a THP. bash 60728 [087] 155865.157116: probe:ktask_run: (ffffffffb7ee7a80) bash 60728 [087] 155865.157119: workqueue:workqueue_queue_work: work struct=0xffff95fb73276000 bash 60728 [087] 155865.157119: workqueue:workqueue_activate_work: work struct 0xffff95fb73276000 kworker/u194:3- 86730 [095] 155865.157168: workqueue:workqueue_execute_start: work struct 0xffff95fb73276000: function ktask_thread kworker/u194:3- 86730 [095] 155865.157170: workqueue:workqueue_execute_end: work struct 0xffff95fb73276000 kworker/u194:3- 86730 [095] 155865.157171: workqueue:workqueue_execute_start: work struct 0xffffa676995bfb90: function wq_barrier_func kworker/u194:3- 86730 [095] 155865.157190: workqueue:workqueue_execute_end: work struct 0xffffa676995bfb90 bash 60728 [087] 155865.157207: probe:ktask_run_ret__return: (ffffffffb7ee7a80 <- ffffffffb7ee7b7b) > > > > It would be nice to multithread at a higher granularity than 2M, too: a range > > of THPs might also perform better than a single page. > > Sure. But the kernel currently does not copy multiple pages altogether even if a range > of THPs is migrated. Page copy function is interleaved with page table operations > for every single page. > > I also did some study and modified the kernel to improve this, which I called > concurrent page migration in https://lwn.net/Articles/714991/. It further > improves page migration throughput. Ok, over 4x with 8 threads for 16 THPs. Is 16 a typical number for migration, or does it get larger? What workloads do you have in mind with this change?