Re: [PATCH 2/2] net/sock: Propagate WF_SYNC only when requested
From: Shrikanth Hegde
Date: Tue Jul 21 2026 - 00:50:52 EST
Hi Srikar,
On 7/14/26 7:09 AM, Srikar Dronamraju wrote:
Use SOCK_SYNC_WAKEUP to select between synchronous and asynchronous wakeup
wakeup APIs. This avoids propagating WF_SYNC when no blocking waiter is
expected. All wakeup locations in networking code that currently issue
synchronous poll-style wakeups unconditionally are updated.
You can also add the performance data in the cover-letter to this patch.
Signed-off-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxx>
---
net/core/sock.c | 31 ++++++++++++++++++++++++-------
net/sctp/socket.c | 10 ++++++++--
net/smc/af_smc.c | 4 ++--
net/smc/smc_rx.c | 10 ++++++++--
net/tipc/socket.c | 22 +++++++++++++++++-----
net/unix/af_unix.c | 26 ++++++++++++++++++--------
6 files changed, 77 insertions(+), 26 deletions(-)
diff --git a/net/core/sock.c b/net/core/sock.c
index 8a59bfaa8096..a214e883b14b 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -3652,9 +3652,15 @@ void sock_def_readable(struct sock *sk)
rcu_read_lock();
wq = rcu_dereference(sk->sk_wq);
- if (skwq_has_sleeper(wq))
- wake_up_interruptible_sync_poll(&wq->wait, EPOLLIN | EPOLLPRI |
+ if (skwq_has_sleeper(wq)) {
+ if (sock_flag(sk, SOCK_SYNC_WAKEUP)) {
+ wake_up_interruptible_sync_poll(&wq->wait, EPOLLIN | EPOLLPRI |
+ EPOLLRDNORM | EPOLLRDBAND);
+ } else {
+ wake_up_interruptible_poll(&wq->wait, EPOLLIN | EPOLLPRI |
EPOLLRDNORM | EPOLLRDBAND);
+ }
+ }
sk_wake_async_rcu(sk, SOCK_WAKE_WAITD, POLL_IN);
rcu_read_unlock();
}
@@ -3670,9 +3676,15 @@ static void sock_def_write_space(struct sock *sk)
*/
if (sock_writeable(sk)) {
wq = rcu_dereference(sk->sk_wq);
- if (skwq_has_sleeper(wq))
- wake_up_interruptible_sync_poll(&wq->wait, EPOLLOUT |
+ if (skwq_has_sleeper(wq)) {
+ if (sock_flag(sk, SOCK_SYNC_WAKEUP)) {
+ wake_up_interruptible_sync_poll(&wq->wait, EPOLLOUT |
+ EPOLLWRNORM | EPOLLWRBAND);
+ } else {
+ wake_up_interruptible_poll(&wq->wait, EPOLLOUT |
EPOLLWRNORM | EPOLLWRBAND);
+ }
+ }
/* Should agree with poll, otherwise some programs break */
sk_wake_async_rcu(sk, SOCK_WAKE_SPACE, POLL_OUT);
@@ -3695,10 +3707,15 @@ static void sock_def_write_space_wfree(struct sock *sk, int wmem_alloc)
/* rely on refcount_sub from sock_wfree() */
smp_mb__after_atomic();
- if (wq && waitqueue_active(&wq->wait))
- wake_up_interruptible_sync_poll(&wq->wait, EPOLLOUT |
+ if (wq && waitqueue_active(&wq->wait)) {
+ if (sock_flag(sk, SOCK_SYNC_WAKEUP)) {
+ wake_up_interruptible_sync_poll(&wq->wait, EPOLLOUT |
EPOLLWRNORM | EPOLLWRBAND);
-
+ } else {
+ wake_up_interruptible_poll(&wq->wait, EPOLLOUT |
+ EPOLLWRNORM | EPOLLWRBAND);
+ }
+ }
/* Should agree with poll, otherwise some programs break */
sk_wake_async_rcu(sk, SOCK_WAKE_SPACE, POLL_OUT);
}
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index c7b9e325ec1c..9cb3432f065a 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -9348,9 +9348,15 @@ void sctp_data_ready(struct sock *sk)
rcu_read_lock();
wq = rcu_dereference(sk->sk_wq);
- if (skwq_has_sleeper(wq))
- wake_up_interruptible_sync_poll(&wq->wait, EPOLLIN |
+ if (skwq_has_sleeper(wq)) {
+ if (sock_flag(sk, SOCK_SYNC_WAKEUP)) {
+ wake_up_interruptible_sync_poll(&wq->wait, EPOLLIN |
+ EPOLLRDNORM | EPOLLRDBAND);
+ } else {
+ wake_up_interruptible_poll(&wq->wait, EPOLLIN |
EPOLLRDNORM | EPOLLRDBAND);
+ }
+ }
sk_wake_async_rcu(sk, SOCK_WAKE_WAITD, POLL_IN);
rcu_read_unlock();
}
diff --git a/net/smc/af_smc.c b/net/smc/af_smc.c
index b5db69073e20..1a6ea2e30769 100644
--- a/net/smc/af_smc.c
+++ b/net/smc/af_smc.c
@@ -819,10 +819,10 @@ static void smc_fback_wakeup_waitqueue(struct smc_sock *smc, void *key)
wake_up_interruptible_all(&wq->wait);
} else {
flags = key_to_poll(key);
- if (flags & (EPOLLIN | EPOLLOUT))
+ if (flags & (EPOLLIN | EPOLLOUT) && sock_flag(&smc->sk, SOCK_SYNC_WAKEUP))
/* sk_data_ready or sk_write_space */
wake_up_interruptible_sync_poll(&wq->wait, flags);
- else if (flags & EPOLLERR)
+ else
/* sk_error_report */
wake_up_interruptible_poll(&wq->wait, flags);
}
diff --git a/net/smc/smc_rx.c b/net/smc/smc_rx.c
index c1d9b923938d..4e288a2364d2 100644
--- a/net/smc/smc_rx.c
+++ b/net/smc/smc_rx.c
@@ -39,9 +39,15 @@ static void smc_rx_wake_up(struct sock *sk)
/* called already in smc_listen_work() */
rcu_read_lock();
wq = rcu_dereference(sk->sk_wq);
- if (skwq_has_sleeper(wq))
- wake_up_interruptible_sync_poll(&wq->wait, EPOLLIN | EPOLLPRI |
+ if (skwq_has_sleeper(wq)) {
+ if (sock_flag(sk, SOCK_SYNC_WAKEUP)) {
+ wake_up_interruptible_sync_poll(&wq->wait, EPOLLIN | EPOLLPRI |
EPOLLRDNORM | EPOLLRDBAND);
+ } else {
+ wake_up_interruptible_poll(&wq->wait, EPOLLIN | EPOLLPRI |
+ EPOLLRDNORM | EPOLLRDBAND);
+ }
+ }
sk_wake_async_rcu(sk, SOCK_WAKE_WAITD, POLL_IN);
if ((sk->sk_shutdown == SHUTDOWN_MASK) ||
(sk->sk_state == SMC_CLOSED))
diff --git a/net/tipc/socket.c b/net/tipc/socket.c
index e564341e0216..9fa83a89882c 100644
--- a/net/tipc/socket.c
+++ b/net/tipc/socket.c
@@ -2116,9 +2116,15 @@ static void tipc_write_space(struct sock *sk)
rcu_read_lock();
wq = rcu_dereference(sk->sk_wq);
- if (skwq_has_sleeper(wq))
- wake_up_interruptible_sync_poll(&wq->wait, EPOLLOUT |
+ if (skwq_has_sleeper(wq)) {
+ if (sock_flag(sk, SOCK_SYNC_WAKEUP)) {
+ wake_up_interruptible_sync_poll(&wq->wait, EPOLLOUT |
EPOLLWRNORM | EPOLLWRBAND);
+ } else {
+ wake_up_interruptible_poll(&wq->wait, EPOLLOUT |
+ EPOLLWRNORM | EPOLLWRBAND);
+ }
+ }
rcu_read_unlock();
}
@@ -2134,9 +2140,15 @@ static void tipc_data_ready(struct sock *sk)
rcu_read_lock();
wq = rcu_dereference(sk->sk_wq);
- if (skwq_has_sleeper(wq))
- wake_up_interruptible_sync_poll(&wq->wait, EPOLLIN |
- EPOLLRDNORM | EPOLLRDBAND);
+ if (skwq_has_sleeper(wq)) {
+ if (sock_flag(sk, SOCK_SYNC_WAKEUP)) {
+ wake_up_interruptible_sync_poll(&wq->wait, EPOLLIN |
+ EPOLLRDNORM | EPOLLRDBAND);
+ } else {
+ wake_up_interruptible_poll(&wq->wait, EPOLLIN |
+ EPOLLRDNORM | EPOLLRDBAND);
+ }
+ }
rcu_read_unlock();
}
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index f7a9d55eee8a..15ebcc2d9d58 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -601,9 +601,15 @@ static void unix_write_space(struct sock *sk)
rcu_read_lock();
if (unix_writable(sk, READ_ONCE(sk->sk_state))) {
wq = rcu_dereference(sk->sk_wq);
- if (skwq_has_sleeper(wq))
- wake_up_interruptible_sync_poll(&wq->wait,
- EPOLLOUT | EPOLLWRNORM | EPOLLWRBAND);
+ if (skwq_has_sleeper(wq)) {
+ if (sock_flag(sk, SOCK_SYNC_WAKEUP)) {
+ wake_up_interruptible_sync_poll(&wq->wait,
+ EPOLLOUT | EPOLLWRNORM | EPOLLWRBAND);
+ } else {
+ wake_up_interruptible_poll(&wq->wait,
+ EPOLLOUT | EPOLLWRNORM | EPOLLWRBAND);
+ }
+ }
sk_wake_async_rcu(sk, SOCK_WAKE_SPACE, POLL_OUT);
}
rcu_read_unlock();
@@ -2603,11 +2609,15 @@ int __unix_dgram_recvmsg(struct sock *sk, struct msghdr *msg, size_t size,
goto out;
}
- if (wq_has_sleeper(&u->peer_wait))
- wake_up_interruptible_sync_poll(&u->peer_wait,
- EPOLLOUT | EPOLLWRNORM |
- EPOLLWRBAND);
-
+ if (wq_has_sleeper(&u->peer_wait)) {
+ if (sock_flag(sk, SOCK_SYNC_WAKEUP)) {
+ wake_up_interruptible_sync_poll(&u->peer_wait,
+ EPOLLOUT | EPOLLWRNORM | EPOLLWRBAND);
+ } else {
+ wake_up_interruptible_poll(&u->peer_wait,
+ EPOLLOUT | EPOLLWRNORM | EPOLLWRBAND);
+ }
+ }
if (msg->msg_name) {
unix_copy_addr(msg, skb->sk);
Would it make sense to write a macro or a wrapper function do the
same instead of sprinkling the same at all the places?
similar comment for patch 1.
IMHO, it would make it easier to read.