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Tue, 31 Aug 2021 13:29:11 -0700 (PDT) X-Google-Smtp-Source: ABdhPJxunpDTehjJtp8uPfbkCYjrgSDEyOXSbca7RCOcPK0k+7So1ajVb2j9QXt9GZsbu5h6ntgAPg== X-Received: by 2002:a05:620a:2a07:: with SMTP id o7mr4820396qkp.213.1630441751258; Tue, 31 Aug 2021 13:29:11 -0700 (PDT) Received: from t490s ([2607:fea8:56a3:500::ad7f]) by smtp.gmail.com with ESMTPSA id a185sm14565129qkg.128.2021.08.31.13.29.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 Aug 2021 13:29:10 -0700 (PDT) Date: Tue, 31 Aug 2021 16:29:09 -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=216.205.24.124; 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=-0.391, 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: , Cc: Elena Ufimtseva , John G Johnson , Jagannathan Raman , qemu-block@nongnu.org, Juan Quintela , "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 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, -- Peter Xu