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io_uring/net: improve the usercopy for sendmsg/recvmsg

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We're spending a considerable amount of the sendmsg/recvmsg time just
copying in the message header. And for provided buffers, the known
single entry iovec.

Be a bit smarter about it and enable/disable user access around our
copying. In a test case that does both sendmsg and recvmsg, the
runtime before this change (averaged over multiple runs, very stable
times however):

Kernel		Time		Diff
====================================
-git		4720 usec
-git+commit	4311 usec	-8.7%

and looking at a profile diff, we see the following:

0.25%     +9.33%  [kernel.kallsyms]     [k] _copy_from_user
4.47%     -3.32%  [kernel.kallsyms]     [k] __io_msg_copy_hdr.constprop.0

where we drop more than 9% of _copy_from_user() time, and consequently
add time to __io_msg_copy_hdr() where the copies are now attributed to,
but with a net win of 6%.

In comparison, the same test case with send/recv runs in 3745 usec, which
is (expectedly) still quite a bit faster. But at least sendmsg/recvmsg is
now only ~13% slower, where it was ~21% slower before.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2024-02-26 16:43:01 -07:00
parent c55978024d
commit 792060de8b
1 changed files with 22 additions and 7 deletions
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29
io_uring/net.c
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@ -255,27 +255,42 @@ static int io_msg_copy_hdr(struct io_kiocb *req, struct io_async_msghdr *iomsg,
struct io_sr_msg *sr = io_kiocb_to_cmd(req, struct io_sr_msg);
int ret;
if (copy_from_user(msg, sr->umsg, sizeof(*sr->umsg)))
if (!user_access_begin(sr->umsg, sizeof(*sr->umsg)))
return -EFAULT;
ret = -EFAULT;
unsafe_get_user(msg->msg_name, &sr->umsg->msg_name, ua_end);
unsafe_get_user(msg->msg_namelen, &sr->umsg->msg_namelen, ua_end);
unsafe_get_user(msg->msg_iov, &sr->umsg->msg_iov, ua_end);
unsafe_get_user(msg->msg_iovlen, &sr->umsg->msg_iovlen, ua_end);
unsafe_get_user(msg->msg_control, &sr->umsg->msg_control, ua_end);
unsafe_get_user(msg->msg_controllen, &sr->umsg->msg_controllen, ua_end);
msg->msg_flags = 0;
if (req->flags & REQ_F_BUFFER_SELECT) {
if (msg->msg_iovlen == 0) {
sr->len = iomsg->fast_iov[0].iov_len = 0;
iomsg->fast_iov[0].iov_base = NULL;
iomsg->free_iov = NULL;
} else if (msg->msg_iovlen > 1) {
return -EINVAL;
ret = -EINVAL;
goto ua_end;
} else {
if (copy_from_user(iomsg->fast_iov, msg->msg_iov,
sizeof(*msg->msg_iov)))
return -EFAULT;
/* we only need the length for provided buffers */
if (!access_ok(&msg->msg_iov[0].iov_len, sizeof(__kernel_size_t)))
goto ua_end;
unsafe_get_user(iomsg->fast_iov[0].iov_len,
&msg->msg_iov[0].iov_len, ua_end);
sr->len = iomsg->fast_iov[0].iov_len;
iomsg->free_iov = NULL;
}
return 0;
ret = 0;
ua_end:
user_access_end();
return ret;
}
user_access_end();
iomsg->free_iov = iomsg->fast_iov;
ret = __import_iovec(ddir, msg->msg_iov, msg->msg_iovlen, UIO_FASTIOV,
&iomsg->free_iov, &iomsg->msg.msg_iter, false);