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Tsirkin" , Jason Wang , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Arseniy Krasnov , "Krasnov Arseniy" CC: "linux-kernel@vger.kernel.org" , "kvm@vger.kernel.org" , "virtualization@lists.linux-foundation.org" , "netdev@vger.kernel.org" , kernel Subject: [RFC PATCH v1 00/12] vsock: MSG_ZEROCOPY flag support Thread-Topic: [RFC PATCH v1 00/12] vsock: MSG_ZEROCOPY flag support Thread-Index: AQHZOfeA2nL8nCs+GE2d7KRGHhlyGw== Date: Mon, 6 Feb 2023 06:51:55 +0000 Message-ID: <0e7c6fc4-b4a6-a27b-36e9-359597bba2b5@sberdevices.ru> Accept-Language: en-US, ru-RU Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [172.16.1.12] Content-ID: <9DBF5BD914616347BBBBC33C6C85928E@sberdevices.ru> MIME-Version: 1.0 X-KSMG-Rule-ID: 4 X-KSMG-Message-Action: clean X-KSMG-AntiSpam-Status: not scanned, disabled by settings X-KSMG-AntiSpam-Interceptor-Info: not scanned X-KSMG-AntiPhishing: not scanned, disabled by settings X-KSMG-AntiVirus: Kaspersky Secure Mail Gateway, version 1.1.2.30, bases: 2023/02/06 01:18:00 #20834045 X-KSMG-AntiVirus-Status: Clean, skipped X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,SPF_HELO_NONE,T_SPF_TEMPERROR autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1757063647023463139?= X-GMAIL-MSGID: =?utf-8?q?1757063647023463139?= Hello, DESCRIPTION this is MSG_ZEROCOPY feature support for virtio/vsock. I tried to follow current implementation for TCP as much as possible: 1) Sender must enable SO_ZEROCOPY flag to use this feature. Without this flag, data will be sent in "classic" copy manner and MSG_ZEROCOPY flag will be ignored (e.g. without completion). 2) Kernel uses completions from socket's error queue. Single completion for single tx syscall (or it can merge several completions to single one). I used already implemented logic for MSG_ZEROCOPY support: 'msg_zerocopy_realloc()' etc. Difference with copy way is not significant. During packet allocation, non-linear skb is created, then I call 'get_user_pages()' for each page from user's iov iterator (I think i don't need 'pin_user_pages()' as there is no backing storage for these pages) and add each returned page to the skb as fragment. There are also some updates for vhost and guest parts of transport - in both cases i've added handling of non-linear skb for virtio part. vhost copies data from such skb to the guest's rx virtio buffers. In the guest, virtio transport fills virtio queue with pages from skb. I think doc in Documentation/networking/msg_zerocopy.rst could be also updated in next versions. This version has several limits/problems: 1) As this feature totally depends on transport, there is no way (or it is difficult) to check whether transport is able to handle it or not during SO_ZEROCOPY setting. Seems I need to call AF_VSOCK specific setsockopt callback from setsockopt callback for SOL_SOCKET, but this leads to lock problem, because both AF_VSOCK and SOL_SOCKET callback are not considered to be called from each other. So in current version SO_ZEROCOPY is set successfully to any type (e.g. transport) of AF_VSOCK socket, but if transport does not support MSG_ZEROCOPY, tx routine will fail with EOPNOTSUPP. 2) When MSG_ZEROCOPY is used, for each tx system call we need to enqueue one completion. In each completion there is flag which shows how tx was performed: zerocopy or copy. This leads that whole message must be send in zerocopy or copy way - we can't send part of message with copying and rest of message with zerocopy mode (or vice versa). Now, we need to account vsock credit logic, e.g. we can't send whole data once - only allowed number of bytes could sent at any moment. In case of copying way there is no problem as in worst case we can send single bytes, but zerocopy is more complex because smallest transmission unit is single page. So if there is not enough space at peer's side to send integer number of pages (at least one) - we will wait, thus stalling tx side. To overcome this problem i've added simple rule - zerocopy is possible only when there is enough space at another side for whole message (to check, that current 'msghdr' was already used in previous tx iterations i use 'iov_offset' field of it's iov iter). 3) loopback transport is not supported, because it requires to implement non-linear skb handling in dequeue logic (as we "send" fragged skb and "receive" it from the same queue). I'm going to implement it in next versions. 4) Current implementation sets max length of packet to 64KB. IIUC this is due to 'kmalloc()' allocated data buffers. I think, in case of MSG_ZEROCOPY this value could be increased, because 'kmalloc()' is not touched for data - user space pages are used as buffers. Also this limit trims every message which is > 64KB, thus such messages will be send in copy mode due to 'iov_offset' check in 2). PERFORMANCE Performance: it is a little bit tricky to compare performance between copy and zerocopy transmissions. In zerocopy way we need to wait when user buffers will be released by kernel, so it something like synchronous path (wait until device driver will process it), while in copy way we can feed data to kernel as many as we want, don't care about device driver. So I compared only time which we spend in 'sendmsg()' syscall. Also there is limit from 4) above so max buffer size is 64KB. I've tested this patchset in the nested VM, but i think for V1 it is not a big deal. Sender: ./vsock_perf --sender --buf-size --bytes 60M [--zc] Receiver: ./vsock_perf --vsk-size 256M Number in cell is seconds which senders spends inside tx syscall. Guest to host transmission: *-------------------------------* | | | | | buf size | copy | zerocopy | | | | | *-------------------------------* | 4KB | 0.26 | 0.042 | *-------------------------------* | 16KB | 0.11 | 0.014 | *-------------------------------* | 32KB | 0.05 | 0.009 | *-------------------------------* | 64KB | 0.04 | 0.005 | *-------------------------------* Host to guest transmission: *--------------------------------* | | | | | buf size | copy | zerocopy | | | | | *--------------------------------* | 4KB | 0.049 | 0.034 | *--------------------------------* | 16KB | 0.03 | 0.024 | *--------------------------------* | 32KB | 0.025 | 0.01 | *--------------------------------* | 64KB | 0.028 | 0.01 | *--------------------------------* If host fails to send data with "Cannot allocate memory", check value /proc/sys/net/core/optmem_max - it is accounted during completion skb allocation. Zerocopy is faster than classic copy mode, but of course it requires specific architecture of application due to user pages pinning, buffer size and alignment. In next versions i'm going to fix 64KB barrier to perform tests with bigger buffer sizes. TESTING This patchset includes set of tests for MSG_ZEROCOPY feature. I tried to cover new code as much as possible so there are different cases for MSG_ZEROCOPY transmissions: with disabled SO_ZEROCOPY and several io vector types (different sizes, alignments, with unmapped pages). Thanks, Arseniy Arseniy Krasnov(12): vsock: check error queue to set EPOLLERR vsock: read from socket's error queue vsock: check for MSG_ZEROCOPY support vhost/vsock: non-linear skb handling support vsock/virtio: non-linear skb support vsock/virtio: non-linear skb handling for TAP dev vsock/virtio: MGS_ZEROCOPY flag support vhost/vsock: support MSG_ZEROCOPY for transport vsock/virtio: support MSG_ZEROCOPY for transport net/sock: enable setting SO_ZEROCOPY for PF_VSOCK test/vsock: MSG_ZEROCOPY flag tests test/vsock: MSG_ZEROCOPY support for vsock_perf drivers/vhost/vsock.c | 62 +++- include/linux/socket.h | 1 + include/linux/virtio_vsock.h | 12 + include/net/af_vsock.h | 2 + net/core/sock.c | 4 +- net/vmw_vsock/af_vsock.c | 35 ++- net/vmw_vsock/virtio_transport.c | 38 ++- net/vmw_vsock/virtio_transport_common.c | 255 ++++++++++++++-- tools/testing/vsock/Makefile | 2 +- tools/testing/vsock/util.h | 1 + tools/testing/vsock/vsock_perf.c | 127 +++++++- tools/testing/vsock/vsock_test.c | 11 + tools/testing/vsock/vsock_test_zerocopy.c | 470 ++++++++++++++++++++++++++++++ tools/testing/vsock/vsock_test_zerocopy.h | 12 + 14 files changed, 991 insertions(+), 41 deletions(-) --- 2.25.1