Re: [PATCH 4/4] io_uring: add netmsg cache

Dylan Yudaken
2022-07-08T07:34:06Z

On Thu, 2022-07-07 at 17:23 -0600, Jens Axboe wrote:
> For recvmsg/sendmsg, if they don't complete inline, we currently need
> to allocate a struct io_async_msghdr for each request. This is a
> somewhat large struct.
>
> Hook up sendmsg/recvmsg to use the io_alloc_cache. This reduces the
> alloc + free overhead considerably, yielding 4-5% of extra
> performance
> running netbench.
>
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> ---
>  include/linux/io_uring_types.h |  6 ++-
>  io_uring/io_uring.c            |  3 ++
>  io_uring/net.c                 | 73 +++++++++++++++++++++++++++++---
> --
>  io_uring/net.h                 | 11 ++++-
>  4 files changed, 81 insertions(+), 12 deletions(-)
>
> diff --git a/include/linux/io_uring_types.h
> b/include/linux/io_uring_types.h
> index bf8f95332eda..d54b8b7e0746 100644
> --- a/include/linux/io_uring_types.h
> +++ b/include/linux/io_uring_types.h
> @@ -222,8 +222,7 @@ struct io_ring_ctx {
>                 struct io_hash_table    cancel_table_locked;
>                 struct list_head        cq_overflow_list;
>                 struct io_alloc_cache   apoll_cache;
> -               struct xarray           personalities;
> -               u32                     pers_next;
> +               struct io_alloc_cache   netmsg_cache;
>         } ____cacheline_aligned_in_smp;
>
>         /* IRQ completion list, under ->completion_lock */
> @@ -241,6 +240,9 @@ struct io_ring_ctx {
>         unsigned int            file_alloc_start;
>         unsigned int            file_alloc_end;
>
> +       struct xarray           personalities;
> +       u32                     pers_next;
> +
>         struct {
>                 /*
>                  * We cache a range of free CQEs we can use, once
> exhausted it
> diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
> index b5098773d924..32110c5b4059 100644
> --- a/io_uring/io_uring.c
> +++ b/io_uring/io_uring.c
> @@ -89,6 +89,7 @@
>  #include "kbuf.h"
>  #include "rsrc.h"
>  #include "cancel.h"
> +#include "net.h"
>
>  #include "timeout.h"
>  #include "poll.h"
> @@ -297,6 +298,7 @@ static __cold struct io_ring_ctx
> *io_ring_ctx_alloc(struct io_uring_params *p)
>         INIT_LIST_HEAD(&ctx->cq_overflow_list);
>         INIT_LIST_HEAD(&ctx->io_buffers_cache);
>         io_alloc_cache_init(&ctx->apoll_cache);
> +       io_alloc_cache_init(&ctx->netmsg_cache);
>         init_completion(&ctx->ref_comp);
>         xa_init_flags(&ctx->personalities, XA_FLAGS_ALLOC1);
>         mutex_init(&ctx->uring_lock);
> @@ -2473,6 +2475,7 @@ static __cold void io_ring_ctx_free(struct
> io_ring_ctx *ctx)
>                 __io_cqring_overflow_flush(ctx, true);
>         io_eventfd_unregister(ctx);
>         io_flush_apoll_cache(ctx);
> +       io_flush_netmsg_cache(ctx);
>         mutex_unlock(&ctx->uring_lock);
>         io_destroy_buffers(ctx);
>         if (ctx->sq_creds)
> diff --git a/io_uring/net.c b/io_uring/net.c
> index 6679069eeef1..ba7e94ff287c 100644
> --- a/io_uring/net.c
> +++ b/io_uring/net.c
> @@ -12,6 +12,7 @@
>
>  #include "io_uring.h"
>  #include "kbuf.h"
> +#include "alloc_cache.h"
>  #include "net.h"
>
>  #if defined(CONFIG_NET)
> @@ -97,18 +98,57 @@ static bool io_net_retry(struct socket *sock, int
> flags)
>         return sock->type == SOCK_STREAM || sock->type ==
> SOCK_SEQPACKET;
>  }
>
> +static void io_netmsg_recycle(struct io_kiocb *req, unsigned int
> issue_flags)
> +{
> +       struct io_async_msghdr *hdr = req->async_data;
> +
> +       if (!hdr || issue_flags & IO_URING_F_UNLOCKED)
> +               return;
> +
> +       if (io_alloc_cache_store(&req->ctx->netmsg_cache)) {
> +               hlist_add_head(&hdr->cache_list, &req->ctx-
> >netmsg_cache.list);

can io_alloc_cache_store just do the store?
would be nicer to have cache::list be generally unused outside of the
cache code.

> +               req->async_data = NULL;
> +               req->flags &= ~REQ_F_ASYNC_DATA;
> +       }
> +}
> +
> +static struct io_async_msghdr *io_recvmsg_alloc_async(struct
> io_kiocb *req,
> +                                                     unsigned int
> issue_flags)
> +{
> +       struct io_ring_ctx *ctx = req->ctx;
> +
> +       if (!(issue_flags & IO_URING_F_UNLOCKED) &&
> +           !hlist_empty(&ctx->netmsg_cache.list)) {
> +               struct io_async_msghdr *hdr;
> +
> +               hdr = hlist_entry(ctx->netmsg_cache.list.first,
> +                                       struct io_async_msghdr,
> cache_list);
> +               ctx->netmsg_cache.nr_cached--;
> +               hlist_del(&hdr->cache_list);

ditto here. I think all the hlist stuff and the nr_cached manipulation
can be wrapped up

> +               req->flags |= REQ_F_ASYNC_DATA;
> +               req->async_data = hdr;
> +               return hdr;
> +       }
> +
> +       if (!io_alloc_async_data(req))
> +               return req->async_data;
> +
> +       return NULL;
> +}
> +
>  static int io_setup_async_msg(struct io_kiocb *req,
> -                             struct io_async_msghdr *kmsg)
> +                             struct io_async_msghdr *kmsg,
> +                             unsigned int issue_flags)
>  {
>         struct io_async_msghdr *async_msg = req->async_data;
>
>         if (async_msg)
>                 return -EAGAIN;
> -       if (io_alloc_async_data(req)) {
> +       async_msg = io_recvmsg_alloc_async(req, issue_flags);
> +       if (!async_msg) {
>                 kfree(kmsg->free_iov);
>                 return -ENOMEM;
>         }
> -       async_msg = req->async_data;
>         req->flags |= REQ_F_NEED_CLEANUP;
>         memcpy(async_msg, kmsg, sizeof(*kmsg));
>         async_msg->msg.msg_name = &async_msg->addr;
> @@ -195,7 +235,7 @@ int io_sendmsg(struct io_kiocb *req, unsigned int
> issue_flags)
>
>         if (!(req->flags & REQ_F_POLLED) &&
>             (sr->flags & IORING_RECVSEND_POLL_FIRST))
> -               return io_setup_async_msg(req, kmsg);
> +               return io_setup_async_msg(req, kmsg, issue_flags);
>
>         flags = sr->msg_flags;
>         if (issue_flags & IO_URING_F_NONBLOCK)
> @@ -207,13 +247,13 @@ int io_sendmsg(struct io_kiocb *req, unsigned
> int issue_flags)
>
>         if (ret < min_ret) {
>                 if (ret == -EAGAIN && (issue_flags &
> IO_URING_F_NONBLOCK))
> -                       return io_setup_async_msg(req, kmsg);
> +                       return io_setup_async_msg(req, kmsg,
> issue_flags);
>                 if (ret == -ERESTARTSYS)
>                         ret = -EINTR;
>                 if (ret > 0 && io_net_retry(sock, flags)) {
>                         sr->done_io += ret;
>                         req->flags |= REQ_F_PARTIAL_IO;
> -                       return io_setup_async_msg(req, kmsg);
> +                       return io_setup_async_msg(req, kmsg,
> issue_flags);
>                 }
>                 req_set_fail(req);
>         }
> @@ -221,6 +261,7 @@ int io_sendmsg(struct io_kiocb *req, unsigned int
> issue_flags)
>         if (kmsg->free_iov)
>                 kfree(kmsg->free_iov);
>         req->flags &= ~REQ_F_NEED_CLEANUP;
> +       io_netmsg_recycle(req, issue_flags);
>         if (ret >= 0)
>                 ret += sr->done_io;
>         else if (sr->done_io)
> @@ -495,7 +536,7 @@ int io_recvmsg(struct io_kiocb *req, unsigned int
> issue_flags)
>
>         if (!(req->flags & REQ_F_POLLED) &&
>             (sr->flags & IORING_RECVSEND_POLL_FIRST))
> -               return io_setup_async_msg(req, kmsg);
> +               return io_setup_async_msg(req, kmsg, issue_flags);
>
>         if (io_do_buffer_select(req)) {
>                 void __user *buf;
> @@ -519,13 +560,13 @@ int io_recvmsg(struct io_kiocb *req, unsigned
> int issue_flags)
>         ret = __sys_recvmsg_sock(sock, &kmsg->msg, sr->umsg, kmsg-
> >uaddr, flags);
>         if (ret < min_ret) {
>                 if (ret == -EAGAIN && force_nonblock)
> -                       return io_setup_async_msg(req, kmsg);
> +                       return io_setup_async_msg(req, kmsg,
> issue_flags);
>                 if (ret == -ERESTARTSYS)
>                         ret = -EINTR;
>                 if (ret > 0 && io_net_retry(sock, flags)) {
>                         sr->done_io += ret;
>                         req->flags |= REQ_F_PARTIAL_IO;
> -                       return io_setup_async_msg(req, kmsg);
> +                       return io_setup_async_msg(req, kmsg,
> issue_flags);
>                 }
>                 req_set_fail(req);
>         } else if ((flags & MSG_WAITALL) && (kmsg->msg.msg_flags &
> (MSG_TRUNC | MSG_CTRUNC))) {
> @@ -535,6 +576,7 @@ int io_recvmsg(struct io_kiocb *req, unsigned int
> issue_flags)
>         /* fast path, check for non-NULL to avoid function call */
>         if (kmsg->free_iov)
>                 kfree(kmsg->free_iov);
> +       io_netmsg_recycle(req, issue_flags);
>         req->flags &= ~REQ_F_NEED_CLEANUP;
>         if (ret > 0)
>                 ret += sr->done_io;
> @@ -848,4 +890,17 @@ int io_connect(struct io_kiocb *req, unsigned
> int issue_flags)
>         io_req_set_res(req, ret, 0);
>         return IOU_OK;
>  }
> +
> +void io_flush_netmsg_cache(struct io_ring_ctx *ctx)
> +{
> +       while (!hlist_empty(&ctx->netmsg_cache.list)) {
> +               struct io_async_msghdr *hdr;
> +
> +               hdr = hlist_entry(ctx->netmsg_cache.list.first,
> +                                       struct io_async_msghdr,
> cache_list);
> +               hlist_del(&hdr->cache_list);
> +               kfree(hdr);
> +       }
> +       ctx->netmsg_cache.nr_cached = 0;
> +}

again - could be put somewhere common. I assume there will not be much
more cleanup than simple kfree

>  #endif
> diff --git a/io_uring/net.h b/io_uring/net.h
> index 81d71d164770..576efb602c7f 100644
> --- a/io_uring/net.h
> +++ b/io_uring/net.h
> @@ -5,7 +5,10 @@
>
>  #if defined(CONFIG_NET)
>  struct io_async_msghdr {
> -       struct iovec                    fast_iov[UIO_FASTIOV];
> +       union {
> +               struct iovec            fast_iov[UIO_FASTIOV];
> +               struct hlist_node       cache_list;
> +       };
>         /* points to an allocated iov, if NULL we use fast_iov
> instead */
>         struct iovec                    *free_iov;
>         struct sockaddr __user          *uaddr;
> @@ -40,4 +43,10 @@ int io_socket(struct io_kiocb *req, unsigned int
> issue_flags);
>  int io_connect_prep_async(struct io_kiocb *req);
>  int io_connect_prep(struct io_kiocb *req, const struct io_uring_sqe
> *sqe);
>  int io_connect(struct io_kiocb *req, unsigned int issue_flags);
> +
> +void io_flush_netmsg_cache(struct io_ring_ctx *ctx);
> +#else
> +static inline void io_flush_netmsg_cache(struct io_ring_ctx *ctx)
> +{
> +}
>  #endif