MEDIUM: connection: only call ->wake() for connect() without I/O
We used to call ->wake() for any I/O event for which there was no
subscriber. But this is a problem because this causes massive wake()
storms since we disabled fd_stop_recv() to save syscalls.
The only reason for the io_available condition is to detect that an
asynchronous connect() just finished and will not be handled by any
registered event handler. Since we now properly handle synchronous
connects, we can detect this situation by the fact that we had a
success on conn_fd_check() and no requested I/O took over.
diff --git a/src/connection.c b/src/connection.c
index ae53d56..fea092b 100644
--- a/src/connection.c
+++ b/src/connection.c
@@ -73,7 +73,7 @@
{
struct connection *conn = fdtab[fd].owner;
unsigned int flags;
- int io_available = 0;
+ int need_wake = 0;
if (unlikely(!conn)) {
activity[tid].conn_dead++;
@@ -91,6 +91,7 @@
*/
if (!conn_fd_check(conn))
goto leave;
+ need_wake = 1;
}
if (fd_send_ready(fd) && fd_send_active(fd)) {
@@ -100,12 +101,12 @@
*/
flags = 0;
if (conn->subs && conn->subs->events & SUB_RETRY_SEND) {
+ need_wake = 0; // wake will be called after this I/O
tasklet_wakeup(conn->subs->tasklet);
conn->subs->events &= ~SUB_RETRY_SEND;
if (!conn->subs->events)
conn->subs = NULL;
- } else
- io_available = 1;
+ }
fd_stop_send(fd);
}
@@ -120,12 +121,12 @@
*/
flags = 0;
if (conn->subs && conn->subs->events & SUB_RETRY_RECV) {
+ need_wake = 0; // wake will be called after this I/O
tasklet_wakeup(conn->subs->tasklet);
conn->subs->events &= ~SUB_RETRY_RECV;
if (!conn->subs->events)
conn->subs = NULL;
- } else
- io_available = 1;
+ }
}
leave:
@@ -152,7 +153,7 @@
* Note that the wake callback is allowed to release the connection and
* the fd (and return < 0 in this case).
*/
- if ((io_available || ((conn->flags ^ flags) & CO_FL_NOTIFY_DONE) ||
+ if ((need_wake || ((conn->flags ^ flags) & CO_FL_NOTIFY_DONE) ||
((flags & CO_FL_WAIT_XPRT) && !(conn->flags & CO_FL_WAIT_XPRT))) &&
conn->mux && conn->mux->wake && conn->mux->wake(conn) < 0)
return;