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=-2.4 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,USER_AGENT_SANE_1 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 88BEFC2D0C2 for ; Fri, 3 Jan 2020 17:34:16 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 502F32085B for ; Fri, 3 Jan 2020 17:34:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Xqpyp1ou" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 502F32085B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:55206 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1inQpz-0005Kq-9I for qemu-devel@archiver.kernel.org; Fri, 03 Jan 2020 12:34:15 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:56660) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1inQoi-0004NA-0D for qemu-devel@nongnu.org; Fri, 03 Jan 2020 12:32:57 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1inQoe-0007Cr-Mf for qemu-devel@nongnu.org; Fri, 03 Jan 2020 12:32:54 -0500 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:37780 helo=us-smtp-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1inQoe-00072s-4J for qemu-devel@nongnu.org; Fri, 03 Jan 2020 12:32:52 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1578072770; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ZQ7wJqhmfP/B5rdYGIUG1wz++qoIaAOgrrO1ZSoihmI=; b=Xqpyp1ouGBU94NHooH94MAXE+tf+YeMXacSEiq7SuhaGSxK7+4YTp+gYswnbne5w5Zl8He h7LED48v0tevDUNv/sr3YEBhWyghP8GrUZSqDaQwq/j2f8sibG5VlBR8D/q4GjOFEyVX26 9rCf9TXkti2VvQHbkk/Sjqqzm7og2fM= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-401-DjQXrk-EM4-uRvnFRmqsTw-1; Fri, 03 Jan 2020 12:32:49 -0500 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id A0F5E800D55 for ; Fri, 3 Jan 2020 17:32:48 +0000 (UTC) Received: from work-vm (ovpn-117-78.ams2.redhat.com [10.36.117.78]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D5AE15C548; Fri, 3 Jan 2020 17:32:46 +0000 (UTC) Date: Fri, 3 Jan 2020 17:32:44 +0000 From: "Dr. David Alan Gilbert" To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Subject: Re: [PATCH v2 01/10] migration: Increase default number of multifd channels to 16 Message-ID: <20200103173244.GQ3804@work-vm> References: <20191218020119.3776-1-quintela@redhat.com> <20191218020119.3776-2-quintela@redhat.com> <20200103165832.GU2753983@redhat.com> <20200103170114.GO3804@work-vm> <20200103171233.GV2753983@redhat.com> MIME-Version: 1.0 In-Reply-To: <20200103171233.GV2753983@redhat.com> User-Agent: Mutt/1.13.0 (2019-11-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-MC-Unique: DjQXrk-EM4-uRvnFRmqsTw-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.120 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Laurent Vivier , Thomas Huth , Eduardo Habkost , Juan Quintela , Markus Armbruster , qemu-devel@nongnu.org, Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Daniel P. Berrang=E9 (berrange@redhat.com) wrote: > On Fri, Jan 03, 2020 at 05:01:14PM +0000, Dr. David Alan Gilbert wrote: > > * Daniel P. Berrang=E9 (berrange@redhat.com) wrote: > > > On Wed, Dec 18, 2019 at 03:01:10AM +0100, Juan Quintela wrote: > > > > We can scale much better with 16, so we can scale to higher numbers= . > > >=20 > > > What was the test scenario showing such scaling ? > > >=20 > > > In the real world I'm sceptical that virt hosts will have > > > 16 otherwise idle CPU cores available that are permissible > > > to use for migration, or indeed whether they'll have network > > > bandwidth available to allow 16 cores to saturate the link. > >=20 > > With TLS or compression, the network bandwidth could easily be there. >=20 > Yes, but this constant is setting a default that applies regardless of > whether TLS / compression is enabled and/or whether CPU cores are idle. > IOW, there can be cases where using 16 threads will be a perf win, I'm > just questioning the suitability as a global default out of the box. >=20 > I feel like what's really lacking with migration is documentation > around the usefulness of the very many parameters, and the various > interesting combinations & tradeoffs around enabling them. So instead > of changing the default threads, can we focusing on improving > documentation so that mgmt apps have good information on which to > make the decision about whether & when to use 2 or 16 or $NNN migration > threads. Yes, although the short answer is; increase it if you find your migration threads are saturated, either due to a very fast network connection, or a CPU heavy setting (such as TLS or compression). The answer to that might also vary if you have compression/encryption offload engines (which I'd like to try). Given that this series is for compression, I guess that's the use Juan is using here. On a 100Gbps NIC (which are readily available these days), I managed to squeeze 70Gbps out of an earlier multifd version with 8 channels, which beat the RDMA code in throughput (albeit eating CPU). Dave > Regards, > Daniel > --=20 > |: https://berrange.com -o- https://www.flickr.com/photos/dberran= ge :| > |: https://libvirt.org -o- https://fstop138.berrange.c= om :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberran= ge :| -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK