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=-15.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 41C95C433EF for ; Wed, 8 Sep 2021 15:29:21 +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 AE0DE610C8 for ; Wed, 8 Sep 2021 15:29:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org AE0DE610C8 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=nongnu.org Received: from localhost ([::1]:39064 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1mNzVn-0004Gt-UI for qemu-devel@archiver.kernel.org; Wed, 08 Sep 2021 11:29:19 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:60790) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mNzTS-00011x-1U for qemu-devel@nongnu.org; Wed, 08 Sep 2021 11:26:57 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:49277) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1mNzTP-0004zF-Ku for qemu-devel@nongnu.org; Wed, 08 Sep 2021 11:26:53 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1631114810; 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=PbzmeEcp4P8e4n7R9kcF7rDGTLBiX7MePObeHG1VYdw=; b=Mn0k2LC25ixAJXKsOzgnWEKJnIye3ay0XdUibVa++SqDI7/sDi0ZyIAno6kbd74noteMmL zOxzAFjXwHq0Vp4P0fe5+Yin1YRNii228w2zerr08HN4xPBtWHUNdDF2PQo58tRZL967+e IaUd5TxgRWe9EfDzea/HE/yqDF4enVY= 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-161-WVK_K9lJNtinYrBHLzCOaQ-1; Wed, 08 Sep 2021 11:26:49 -0400 X-MC-Unique: WVK_K9lJNtinYrBHLzCOaQ-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1873E19057B2; Wed, 8 Sep 2021 15:26:48 +0000 (UTC) Received: from redhat.com (unknown [10.39.193.206]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8992F10016FE; Wed, 8 Sep 2021 15:26:33 +0000 (UTC) Date: Wed, 8 Sep 2021 16:26:31 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: "Dr. David Alan Gilbert" Subject: Re: [PATCH v1 3/3] migration: multifd: Enable zerocopy Message-ID: References: <20210831110238.299458-1-leobras@redhat.com> <20210831110238.299458-4-leobras@redhat.com> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/2.0.7 (2021-05-04) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.393, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action 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: Elena Ufimtseva , John G Johnson , Jagannathan Raman , qemu-block@nongnu.org, Juan Quintela , Jason Wang , qemu-devel@nongnu.org, Peter Xu , Leonardo Bras , Paolo Bonzini , =?utf-8?Q?Marc-Andr=C3=A9?= Lureau , Fam Zheng Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Sep 07, 2021 at 12:13:28PM +0100, Dr. David Alan Gilbert wrote: > * Daniel P. Berrangé (berrange@redhat.com) wrote: > > On Wed, Sep 01, 2021 at 11:35:33AM -0400, Peter Xu wrote: > > > On Wed, Sep 01, 2021 at 09:53:07AM +0100, Daniel P. Berrangé wrote: > > > > On Tue, Aug 31, 2021 at 04:29:09PM -0400, Peter Xu wrote: > > > > > On Tue, Aug 31, 2021 at 02:16:42PM +0100, Daniel P. Berrangé wrote: > > > > > > On Tue, Aug 31, 2021 at 08:02:39AM -0300, Leonardo Bras wrote: > > > > > > > Call qio_channel_set_zerocopy(true) in the start of every multifd thread. > > > > > > > > > > > > > > Change the send_write() interface of multifd, allowing it to pass down > > > > > > > flags for qio_channel_write*(). > > > > > > > > > > > > > > Pass down MSG_ZEROCOPY flag for sending memory pages, while keeping the > > > > > > > other data being sent at the default copying approach. > > > > > > > > > > > > > > Signed-off-by: Leonardo Bras > > > > > > > --- > > > > > > > migration/multifd-zlib.c | 7 ++++--- > > > > > > > migration/multifd-zstd.c | 7 ++++--- > > > > > > > migration/multifd.c | 9 ++++++--- > > > > > > > migration/multifd.h | 3 ++- > > > > > > > 4 files changed, 16 insertions(+), 10 deletions(-) > > > > > > > > > > > > > @@ -675,7 +676,8 @@ static void *multifd_send_thread(void *opaque) > > > > > > > } > > > > > > > > > > > > > > if (used) { > > > > > > > - ret = multifd_send_state->ops->send_write(p, used, &local_err); > > > > > > > + ret = multifd_send_state->ops->send_write(p, used, MSG_ZEROCOPY, > > > > > > > + &local_err); > > > > > > > > > > > > I don't think it is valid to unconditionally enable this feature due to the > > > > > > resource usage implications > > > > > > > > > > > > https://www.kernel.org/doc/html/v5.4/networking/msg_zerocopy.html > > > > > > > > > > > > "A zerocopy failure will return -1 with errno ENOBUFS. This happens > > > > > > if the socket option was not set, the socket exceeds its optmem > > > > > > limit or the user exceeds its ulimit on locked pages." > > > > > > > > > > > > The limit on locked pages is something that looks very likely to be > > > > > > exceeded unless you happen to be running a QEMU config that already > > > > > > implies locked memory (eg PCI assignment) > > > > > > > > > > Yes it would be great to be a migration capability in parallel to multifd. At > > > > > initial phase if it's easy to be implemented on multi-fd only, we can add a > > > > > dependency between the caps. In the future we can remove that dependency when > > > > > the code is ready to go without multifd. Thanks, > > > > > > > > Also, I'm wondering how zerocopy support interacts with kernel support > > > > for kTLS and multipath-TCP, both of which we want to be able to use > > > > with migration. > > > > > > Copying Jason Wang for net implications between these features on kernel side > > > and whether they can be enabled together (MSG_ZEROCOPY, mptcp, kTLS). > > > > > > From the safe side we may want to only enable one of them until we prove > > > they'll work together I guess.. > > > > MPTCP is good when we're network limited for migration > > > > KTLS will be good when we're CPU limited on AES for migration, > > which is essentially always when TLS is used. > > > > ZEROCOPY will be good when we're CPU limited for data copy > > on migration, or to reduce the impact on other concurrent > > VMs on the same CPUs. > > > > Ultimately we woudld benefit from all of them at the same > > time, if it were technically possible todo. > > I think last time I spoke to Paolo Abeni there were some interactions > between them; I can't remember what though (I think mptcp and ktls > didn't play at the time). MPTCP and KTLS use the same kernel hook in the network layer and only 1 hook is permitted at a time, making them mutually exclusive for now. In theory this can be fixed but no one is actively working on it yet. Regards, Daniel -- |: 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 :|