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 C1826C2D0C2 for ; Fri, 3 Jan 2020 17:13:39 +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 8C41920866 for ; Fri, 3 Jan 2020 17:13:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="FDflE1nr" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8C41920866 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]:55020 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1inQW2-0004zv-KK for qemu-devel@archiver.kernel.org; Fri, 03 Jan 2020 12:13:38 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:42120) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1inQVE-00049f-UL for qemu-devel@nongnu.org; Fri, 03 Jan 2020 12:12:50 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1inQVC-0003vX-DH for qemu-devel@nongnu.org; Fri, 03 Jan 2020 12:12:47 -0500 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:56262 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1inQVB-0003i3-4f for qemu-devel@nongnu.org; Fri, 03 Jan 2020 12:12:46 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1578071563; h=from:from:reply-to: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=QEffvvo7Es4RjlDoTyTJ2GskHTOHygG8naX2MvCvuB8=; b=FDflE1nrwNXK7HN2aLS0bnRsfIkM8tIUKeyXdDGRyGw+OmwlJdOr0OmLB1e7TsPDUmdu0K 3NmW6dFEiTLGUS0g+E7URsrJQgZrTylbsc/QFs7CFjI1YhTyOVo4wT9umlJyB1flmI2t4n Z2UzPPcNawO4E+SDKIeeYPz4oAFCFXU= 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-323-dRqCcxrlNmm3ooUT2jpCXw-1; Fri, 03 Jan 2020 12:12:40 -0500 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id E5D48800EB6 for ; Fri, 3 Jan 2020 17:12:38 +0000 (UTC) Received: from redhat.com (ovpn-112-41.ams2.redhat.com [10.36.112.41]) by smtp.corp.redhat.com (Postfix) with ESMTPS id ACF92387; Fri, 3 Jan 2020 17:12:36 +0000 (UTC) Date: Fri, 3 Jan 2020 17:12:33 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: "Dr. David Alan Gilbert" Subject: Re: [PATCH v2 01/10] migration: Increase default number of multifd channels to 16 Message-ID: <20200103171233.GV2753983@redhat.com> References: <20191218020119.3776-1-quintela@redhat.com> <20191218020119.3776-2-quintela@redhat.com> <20200103165832.GU2753983@redhat.com> <20200103170114.GO3804@work-vm> MIME-Version: 1.0 In-Reply-To: <20200103170114.GO3804@work-vm> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-MC-Unique: dRqCcxrlNmm3ooUT2jpCXw-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=utf-8 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: 207.211.31.81 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= 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" On Fri, Jan 03, 2020 at 05:01:14PM +0000, Dr. David Alan Gilbert wrote: > * Daniel P. Berrang=C3=A9 (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. 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. 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. Regards, Daniel --=20 |: https://berrange.com -o- https://www.flickr.com/photos/dberrange= :| |: https://libvirt.org -o- https://fstop138.berrange.com= :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange= :|