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Fri, 24 Mar 2023 17:20:37 +0000 (UTC) Received: from redhat.com (unknown [10.39.194.43]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 09F012A68; Fri, 24 Mar 2023 17:20:35 +0000 (UTC) Date: Fri, 24 Mar 2023 18:20:34 +0100 From: Kevin Wolf To: Florian Westphal Cc: qemu-block@nongnu.org, eblake@redhat.com, vsementsov@yandex-team.ru, qemu-devel@nongnu.org Subject: Re: [PATCH 1/1] nbd/server: push pending frames after sending reply Message-ID: References: <20230324104720.2498-1-fw@strlen.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230324104720.2498-1-fw@strlen.de> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 Received-SPF: pass client-ip=170.10.129.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, 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: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Am 24.03.2023 um 11:47 hat Florian Westphal geschrieben: > qemu-nbd doesn't set TCP_NODELAY on the tcp socket. > > Kernel waits for more data and avoids transmission of small packets. > Without TLS this is barely noticeable, but with TLS this really shows. > > Booting a VM via qemu-nbd on localhost (with tls) takes more than > 2 minutes on my system. tcpdump shows frequent wait periods, where no > packets get sent for a 40ms period. > > Add explicit (un)corking when processing (and responding to) requests. > "TCP_CORK, &zero" after earlier "CORK, &one" will flush pending data. > > VM Boot time: > main: no tls: 23s, with tls: 2m45s > patched: no tls: 14s, with tls: 15s > > VM Boot time, qemu-nbd via network (same lan): > main: no tls: 18s, with tls: 1m50s > patched: no tls: 17s, with tls: 18s > > Future optimization: if we could detect if there is another pending > request we could defer the uncork operation because more data would be > appended. > > Signed-off-by: Florian Westphal > --- > nbd/server.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/nbd/server.c b/nbd/server.c > index a4750e41880a..848836d41405 100644 > --- a/nbd/server.c > +++ b/nbd/server.c > @@ -2667,6 +2667,8 @@ static coroutine_fn void nbd_trip(void *opaque) > goto disconnect; > } > > + qio_channel_set_cork(client->ioc, true); > + > if (ret < 0) { > /* It wasn't -EIO, so, according to nbd_co_receive_request() > * semantics, we should return the error to the client. */ > @@ -2692,6 +2694,7 @@ static coroutine_fn void nbd_trip(void *opaque) > goto disconnect; > } > > + qio_channel_set_cork(client->ioc, false); > done: > nbd_request_put(req); > nbd_client_put(client); In the error paths, we never call set_cork(false) again. I suppose the reason that this is okay is because the next thing is actually that we close the socket? Kevin