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Message-ID: <763c70c4-9f24-150d-64b6-70d6e23f9325@sberdevices.ru> Date: Sat, 1 Jul 2023 09:45:20 +0300 From: Arseniy Krasnov <avkrasnov@...rdevices.ru> To: Stefan Hajnoczi <stefanha@...hat.com>, Stefano Garzarella <sgarzare@...hat.com>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>, Bobby Eshleman <bobby.eshleman@...edance.com> CC: <kvm@...r.kernel.org>, <virtualization@...ts.linux-foundation.org>, <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>, <kernel@...rdevices.ru>, <oxffffaa@...il.com> Subject: Re: [RFC PATCH v5 00/17] vsock: MSG_ZEROCOPY flag support RESEND in https://lore.kernel.org/netdev/20230701063947.3422088-1-AVKrasnov@sberdevices.ru Please ignore this thread Thanks, Arseniy On 01.07.2023 09:22, Arseniy Krasnov wrote: > 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 and filled with pinned user pages. > 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 tx virtio queue with pages from skb. > > Head of this patchset is: > https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=d20dd0ea14072e8a90ff864b2c1603bd68920b4b > > > This version has several limits/problems (all resolved at v5): > > 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. > > ^^^ fixed in v5. Thanks to Bobby Eshleman. > > 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). > > ^^^ > Discussed as ok during v2. Link: > https://lore.kernel.org/netdev/23guh3txkghxpgcrcjx7h62qsoj3xgjhfzgtbmqp2slrz3rxr4@zya2z7kwt75l/ > > 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. > > ^^^ fixed in v2 > > 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). > > ^^^ fixed in v2 > > PATCHSET STRUCTURE > > Patchset has the following structure: > 1) Handle non-linear skbuff on receive in virtio/vhost. > 2) Handle non-linear skbuff on send in virtio/vhost. > 3) Updates for AF_VSOCK. > 4) Enable MSG_ZEROCOPY support on transports. > 5) Tests/tools/docs updates. > > 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 is 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 the 'send()' syscall. > Then if this value will be combined with total number of transmitted > bytes, we can get Gbit/s parameter. Also to avoid tx stalls due to not > enough credit, receiver allocates same amount of space as sender needs. > > Sender: > ./vsock_perf --sender <CID> --buf-size <buf size> --bytes 256M [--zc] > > Receiver: > ./vsock_perf --vsk-size 256M > > I run tests on two setups: desktop with Core i7 - I use this PC for > development and in this case guest is nested guest, and host is normal > guest. Another hardware is some embedded board with Atom - here I don't > have nested virtualization - host runs on hw, and guest is normal guest. > > G2H transmission (values are Gbit/s): > > Core i7 with nested guest. Atom with normal guest. > > *-------------------------------* *-------------------------------* > | | | | | | | | > | buf size | copy | zerocopy | | buf size | copy | zerocopy | > | | | | | | | | > *-------------------------------* *-------------------------------* > | 4KB | 3 | 10 | | 4KB | 0.8 | 1.9 | > *-------------------------------* *-------------------------------* > | 32KB | 20 | 61 | | 32KB | 6.8 | 20.2 | > *-------------------------------* *-------------------------------* > | 256KB | 33 | 244 | | 256KB | 7.8 | 55 | > *-------------------------------* *-------------------------------* > | 1M | 30 | 373 | | 1M | 7 | 95 | > *-------------------------------* *-------------------------------* > | 8M | 22 | 475 | | 8M | 7 | 114 | > *-------------------------------* *-------------------------------* > > H2G: > > Core i7 with nested guest. Atom with normal guest. > > *-------------------------------* *-------------------------------* > | | | | | | | | > | buf size | copy | zerocopy | | buf size | copy | zerocopy | > | | | | | | | | > *-------------------------------* *-------------------------------* > | 4KB | 20 | 10 | | 4KB | 4.37 | 3 | > *-------------------------------* *-------------------------------* > | 32KB | 37 | 75 | | 32KB | 11 | 18 | > *-------------------------------* *-------------------------------* > | 256KB | 44 | 299 | | 256KB | 11 | 62 | > *-------------------------------* *-------------------------------* > | 1M | 28 | 335 | | 1M | 9 | 77 | > *-------------------------------* *-------------------------------* > | 8M | 27 | 417 | | 8M | 9.35 | 115 | > *-------------------------------* *-------------------------------* > > * Let's look to the first line of both tables - where copy is better > than zerocopy. I analyzed this case more deeply and found that > bottleneck is function 'vhost_work_queue()'. With 4K buffer size, > caller spends too much time in it with zerocopy mode (comparing to > copy mode). This happens only with 4K buffer size. This function just > calls 'wake_up_process()' and its internal logic does not depends on > skb, so i think potential reason (may be) is interval between two > calls of this function (e.g. how often it is called). Note, that > 'vhost_work_queue()' differs from the same function at guest's side of > transport: 'virtio_transport_send_pkt()' uses 'queue_work()' which > i think is more optimized for worker purposes, than direct call to > 'wake_up_process()'. But again - this is just my assumption. > > Loopback: > > Core i7 with nested guest. Atom with normal guest. > > *-------------------------------* *-------------------------------* > | | | | | | | | > | buf size | copy | zerocopy | | buf size | copy | zerocopy | > | | | | | | | | > *-------------------------------* *-------------------------------* > | 4KB | 8 | 7 | | 4KB | 1.8 | 1.3 | > *-------------------------------* *-------------------------------* > | 32KB | 38 | 44 | | 32KB | 10 | 10 | > *-------------------------------* *-------------------------------* > | 256KB | 55 | 168 | | 256KB | 15 | 36 | > *-------------------------------* *-------------------------------* > | 1M | 53 | 250 | | 1M | 12 | 45 | > *-------------------------------* *-------------------------------* > | 8M | 40 | 344 | | 8M | 11 | 74 | > *-------------------------------* *-------------------------------* > > I analyzed performace difference more deeply for the following setup: > server: ./vsock_perf --vsk-size 16M > client: ./vsock_perf --sender 2 --bytes 16M --buf-size 16K/4K [--zc] > > In other words I send 16M of data from guest to host in copy/zerocopy > modes and with two different sizes of buffer - 4K and 64K. Let's see > to tx path for both modes - it consists of two steps: > > copy: > 1) Allocate skb of buffer's length. > 2) Copy data to skb from buffer. > > zerocopy: > 1) Allocate skb with header space only. > 2) Pin pages of the buffer and insert them to skb. > > I measured average number of ns (returned by 'ktime_get()') for each > step above: > 1) Skb allocation (for both copy and zerocopy modes). > 2) For copy mode in 'memcpy_to_msg()' - copying. > 3) For zerocopy mode in '__zerocopy_sg_from_iter()' - pinning. > > Here are results for copy mode: > *-------------------------------------* > | buf | skb alloc | 'memcpy_to_msg()' | > *-------------------------------------* > | | | | > | 64K | 5000ns | 25000ns | > | | | | > *-------------------------------------* > | | | | > | 4K | 800ns | 2200ns | > | | | | > *-------------------------------------* > > Here are results for zerocopy mode: > *-----------------------------------------------* > | buf | skb alloc | '__zerocopy_sg_from_iter()' | > *-----------------------------------------------* > | | | | > | 64K | 250ns | 3500ns | > | | | | > *-----------------------------------------------* > | | | | > | 4K | 250ns | 3000ns | > | | | | > *-----------------------------------------------* > > I guess that reason of zerocopy performance is low overhead for page > pinning: there is big difference between 4K and 64K in case of copying > (25000 vs 2200), but in pinning case - just 3000 vs 3500. > > So, 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. > > NOTES > > 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. Try to update it to for example 1M and try send again: > "echo 1048576 > /proc/sys/net/core/optmem_max" (as root). > > 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). I also > run tests with loopback transport and run vsockmon. In v3 i've added > io_uring test as separated application. > > LET'S SPLIT PATCHSET TO MAKE REVIEW EASIER > > In v3 Stefano Garzarella <sgarzare@...hat.com> asked to split this patchset > for several parts, because it looks too big for review. I think in this > version (v4) we can do it in the following way: > > [0001 - 0005] - this is preparation for virtio/vhost part. > [0006 - 0009] - this is preparation for AF_VSOCK part. > [0010 - 0014] - these patches allows to trigger logic from the previous > two parts. In addition 0014 is patch for Documentation. > [0015 - rest] - updates for tests, utils. This part doesn't touch kernel > code and looks not critical. > > Thanks, Arseniy > > Link to v1: > https://lore.kernel.org/netdev/0e7c6fc4-b4a6-a27b-36e9-359597bba2b5@sberdevices.ru/ > Link to v2: > https://lore.kernel.org/netdev/20230423192643.1537470-1-AVKrasnov@sberdevices.ru/ > Link to v3: > https://lore.kernel.org/netdev/20230522073950.3574171-1-AVKrasnov@sberdevices.ru/ > Link to v4: > https://lore.kernel.org/netdev/20230603204939.1598818-1-AVKrasnov@sberdevices.ru/ > > Changelog: > v1 -> v2: > - Replace 'get_user_pages()' with 'pin_user_pages()'. > - Loopback transport support. > > v2 -> v3 > - Use 'get_user_pages()' instead of 'pin_user_pages()'. I think this > is right approach, because i'm using '__zerocopy_sg_from_iter()' > function. It is already implemented and used by io_uring zerocopy > tx logic to 'pin' pages of user's buffer. > > - Use 'skb_copy_datagram_iter()' to copy data from both linear and > non-linear skb to user's iov iter. It already has support for copying > data from paged part of skb (by calling 'kmap()'). In v2 i used my > own "from scratch" implemented function. With this and previous thing > I significantly reduced LOC number in kernel part. > > - Add io_uring test for AF_VSOCK. It is implemented as separated util, > because it depends on liburing (i think there is no need to link > 'vsock_test' with liburing, because io_uring functionality depends > on environment - both in kernel and userspace). > > - Values from PERFORMANCE section are updated for all transports, but > I didn't found any significant difference with v2. > > - More details in commit messages. > > v3 -> v4: > - Requirement for buffers to have page aligned base and size is removed, > because virtio can handle such buffers. > > - Crash with SOCK_SEQPACKET is fixed. This is done by setting owner of > new 'skb' before passing it to '__zerocopy_sg_from_iter()'. Last one > dereferences owner of the passed skb without any checks (it was NULL). > > - Type of "owning" of the newly created skb is also changed: in v3 and > before it was 'skb_set_owner_sk_safe()'. I replace it with this one: > 'skb_set_owner_w()'. This is because '__zerocopy_sg_from_iter()' > increments 'sk_wmem_alloc' of socket which owns skb, thus we need a > proper destructor which decrements it back - it is 'sock_wfree()'. > This destructor is set by 'skb_set_owner_w()'. Otherwise we get leak > of resource - such socket will be never deallocated. > > - Use ITER_KVEC instead of ITER_IOVEC when skb is copied to another one > for passing to TAP device. Reason of this update is that ITER_IOVEC > considered as userspace memory, while we have only kernel memory here. > > v4 -> v5: > - Problem 1) with dependency of SO_ZEROCOPY from the current transport > is fixed. > > - See per patch changelog (after ---). > > Arseniy Krasnov (17): > vsock/virtio: read data from non-linear skb > vhost/vsock: read data from non-linear skb > vsock/virtio: support to send non-linear skb > vsock/virtio: non-linear skb handling for tap > vsock/virtio: MSG_ZEROCOPY flag support > vsock: fix EPOLLERR set on non-empty error queue > vsock: read from socket's error queue > vsock: check for MSG_ZEROCOPY support on send > vsock: enable SOCK_SUPPORT_ZC bit > vhost/vsock: support MSG_ZEROCOPY for transport > vsock/virtio: support MSG_ZEROCOPY for transport > vsock/loopback: support MSG_ZEROCOPY for transport > vsock: enable setting SO_ZEROCOPY > docs: net: description of MSG_ZEROCOPY for AF_VSOCK > test/vsock: MSG_ZEROCOPY flag tests > test/vsock: MSG_ZEROCOPY support for vsock_perf > test/vsock: io_uring rx/tx tests > > Documentation/networking/msg_zerocopy.rst | 12 +- > drivers/vhost/vsock.c | 21 +- > include/linux/socket.h | 1 + > include/linux/virtio_vsock.h | 1 + > include/net/af_vsock.h | 7 + > net/vmw_vsock/af_vsock.c | 61 +++- > net/vmw_vsock/virtio_transport.c | 47 +++- > net/vmw_vsock/virtio_transport_common.c | 313 ++++++++++++++++----- > net/vmw_vsock/vsock_loopback.c | 6 + > tools/testing/vsock/Makefile | 9 +- > tools/testing/vsock/util.c | 218 +++++++++++++++ > tools/testing/vsock/util.h | 18 ++ > tools/testing/vsock/vsock_perf.c | 139 +++++++++- > tools/testing/vsock/vsock_test.c | 16 ++ > tools/testing/vsock/vsock_test_zerocopy.c | 312 +++++++++++++++++++++ > tools/testing/vsock/vsock_test_zerocopy.h | 15 + > tools/testing/vsock/vsock_uring_test.c | 321 ++++++++++++++++++++++ > 17 files changed, 1423 insertions(+), 94 deletions(-) > create mode 100644 tools/testing/vsock/vsock_test_zerocopy.c > create mode 100644 tools/testing/vsock/vsock_test_zerocopy.h > create mode 100644 tools/testing/vsock/vsock_uring_test.c >
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