[PATCH 5.4 35/84] tcp: return EPOLLOUT from tcp_poll only when notsent_bytes is half the limit

Greg Kroah-Hartman
2024-02-27T14:23:05Z

From: Soheil Hassas Yeganeh <soheil@google.com>

[ Upstream commit 8ba3c9d1c6d75d1e6af2087278b30e17f68e1fff ]

If there was any event available on the TCP socket, tcp_poll()
will be called to retrieve all the events. In tcp_poll(), we call
sk_stream_is_writeable() which returns true as long as we are at least
one byte below notsent_lowat. This will result in quite a few
spurious EPLLOUT and frequent tiny sendmsg() calls as a result.

Similar to sk_stream_write_space(), use __sk_stream_is_writeable
with a wake value of 1, so that we set EPOLLOUT only if half the
space is available for write.

Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/ipv4/tcp.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 6a52fdcf9e4ef..e45c09977c600 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -566,7 +566,7 @@ __poll_t tcp_poll(struct file *file, struct socket *sock, poll_table *wait)
mask |= EPOLLIN | EPOLLRDNORM;

if (!(sk->sk_shutdown & SEND_SHUTDOWN)) {
- if (sk_stream_is_writeable(sk)) {
+ if (__sk_stream_is_writeable(sk, 1)) {
mask |= EPOLLOUT | EPOLLWRNORM;
} else { /* send SIGIO later */
sk_set_bit(SOCKWQ_ASYNC_NOSPACE, sk);
@@ -578,7 +578,7 @@ __poll_t tcp_poll(struct file *file, struct socket *sock, poll_table *wait)
* pairs with the input side.
*/
smp_mb__after_atomic();
- if (sk_stream_is_writeable(sk))
+ if (__sk_stream_is_writeable(sk, 1))
mask |= EPOLLOUT | EPOLLWRNORM;
}
} else
--
2.43.0