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[164.138.29.33]) by smtp.gmail.com with ESMTPSA id qw16-20020a1709066a1000b00a3edb758561sm9399668ejc.129.2024.03.08.08.24.41 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Fri, 08 Mar 2024 08:24:41 -0800 (PST) Date: Fri, 8 Mar 2024 17:24:07 +0100 From: Stefano Brivio To: Laurent Vivier Subject: Re: [PATCH 0/4] Some improvements to the tap send path Message-ID: <20240308172407.71c95f07@elisabeth> In-Reply-To: <63786860-6caa-40b3-a432-9a5399636af5@redhat.com> References: <20240308065325.2181322-1-david@gibson.dropbear.id.au> <348a52c9-7c07-4150-b594-4743c7775be6@redhat.com> <20240308093404.3328ad2a@elisabeth> <63786860-6caa-40b3-a432-9a5399636af5@redhat.com> Organization: Red Hat X-Mailer: Claws Mail 4.2.0 (GTK 3.24.36; x86_64-pc-linux-gnu) MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-ID-Hash: 2KE3WNTMRJNQGS4XF3DTGWYGBTKKOCAA X-Message-ID-Hash: 2KE3WNTMRJNQGS4XF3DTGWYGBTKKOCAA X-MailFrom: sbrivio@redhat.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: David Gibson , passt-dev@passt.top X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: On Fri, 8 Mar 2024 16:49:20 +0100 Laurent Vivier wrote: > On 3/8/24 09:34, Stefano Brivio wrote: > > On Fri, 8 Mar 2024 09:18:48 +0100 > > Laurent Vivier wrote: > > > >> On 3/8/24 07:53, David Gibson wrote: > >>> This series has a handful of small improvements to the tap send path. > >>> See individual commit messages for the details. > >>> > >>> I expect this will conflict with Laurent's upcoming work. I hope the > >>> conflicts won't be too bad, and indeed will set us up for less > >>> duplication there in the end. > >> > >> I'm working on patch that devides TCP buffers in several buffers pointed out by an IOV > >> arrays and then provided to tap_send_frames(). I'm going to base my patch on this series. > >> > >> The idea is: > >> > >> A frame is made with 4 iovecs: > >> > >> #define TCP_IOV_VNET 0 > >> #define TCP_IOV_ETH 1 > >> #define TCP_IOV_IP 2 > >> #define TCP_IOV_PAYLOAD 3 > >> #define TCP_IOV_NUM 4 > >> typedef struct iovec tap_iovec_t[TCP_IOV_NUM]; > > > > Except for the typedef :) (I'm actively trying to discourage them) > > ...this looks very neat. > > > > I would suggest that as soon as you have something barely spitting out > > pseudo-correct bytes, you give it a try with perf(1). I'm quite > > concerned that we might end up killing throughput, especially without > > vhost-user, even though in theory it all sounds nice and byte-saving. > > > > Using iovec improves performance: > > iperf3 -c localhost -p 10001 -t 60 -4 > > iovec > > [ 5] 0.00-60.00 sec 32.9 GBytes 4.72 Gbits/sec 0 sender > [ 5] 0.00-60.06 sec 32.9 GBytes 4.71 Gbits/sec receiver > > buf_t > > [ 5] 0.00-60.00 sec 15.9 GBytes 2.27 Gbits/sec 0 sender > [ 5] 0.00-60.06 sec 15.9 GBytes 2.27 Gbits/sec receiver ! ...it must be some alignment matter. Nice. I guess it doesn't happen with large windows (-w ...) or messages (-l 1M), but it looks promising enough with small ones. -- Stefano