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Wed, 01 Sep 2021 08:35:36 -0700 (PDT) X-Google-Smtp-Source: ABdhPJzA9Ms0UnrncxjXL6/uLh49a0eYdl0/hg3Z+GAiXX2/ZgvonLl7pPKx0YNXAUhCssoIAAb8nQ== X-Received: by 2002:a37:b686:: with SMTP id g128mr253924qkf.68.1630510535738; Wed, 01 Sep 2021 08:35:35 -0700 (PDT) Received: from t490s ([2607:fea8:56a3:500::ad7f]) by smtp.gmail.com with ESMTPSA id l7sm215318qki.99.2021.09.01.08.35.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Sep 2021 08:35:35 -0700 (PDT) Date: Wed, 1 Sep 2021 11:35:33 -0400 From: Peter Xu To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= 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: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=peterx@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=170.10.133.124; envelope-from=peterx@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=-0.392, 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=ham 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: , Cc: Elena Ufimtseva , John G Johnson , Jagannathan Raman , qemu-block@nongnu.org, Juan Quintela , Jason Wang , "Dr. David Alan Gilbert" , qemu-devel@nongnu.org, 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 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.. Not a immediate concern as I don't really think any of them is really explicitly supported in qemu. KTLS may be implicitly included by a new gnutls, but we need to mark TLS and ZEROCOPY mutual exclusive anyway because at least the userspace TLS code of gnutls won't has a way to maintain the tls buffers used by zerocopy. So at least we need some knob to detect whether kTLS is enabled in gnutls. -- Peter Xu