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OPTIM: stconn: Don't pretend mux have more data to deliver on EOI/EOS/ERROR

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Doing some benchs on the 3.0, we encountered a small loss on requests/sec on
small objects compared to the 2.8 . After bisecting the issue, it appeared
that this was introduced when the mux-to-mux zero-copy data forwarding was
implemented in 2.9-dev8. Extra subscribes on receives at the end of the
message were responsible of the loss.

A basic configuration, sending H2 requests to a H1 server returning
responses without payload is enough to observe the issue. With the following
command, we can observe a huge increase of epoll_ctl calls on 2.9/3.x:

  h2load -c 100 -m 10 -n 100000 http://...

On 2.8 we have around 3200 calls to epoll_ctl against more than 20k on 3.1.

The fix seems obvious. After a receive, there is no reason to state a mux
have more data to deliver if EOI/EOS/ERROR flag was set on the
stream-endpoint descriptor. With this change, extra calls to epoll_ctl
disappear. However it is a sensitive part so it is important to keep an eye
on it and to not backport it.

Thanks to Willy and Emeric to have spot the issue.
This commit is contained in:
Christopher Faulet 2024-09-27 15:05:11 +02:00
parent 11051ed9c7
commit bca5e14235
1 changed files with 16 additions and 2 deletions
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18
src/stconn.c
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@ -1520,19 +1520,33 @@ int sc_conn_recv(struct stconn *sc)
sc_conn_eos(sc); sc_conn_eos(sc);
ret = 1; ret = 1;
} }
if (sc_ep_test(sc, SE_FL_ERROR)) { if (sc_ep_test(sc, SE_FL_ERROR)) {
sc->flags |= SC_FL_ERROR; sc->flags |= SC_FL_ERROR;
ret = 1; ret = 1;
} }
if (sc->flags & (SC_FL_EOS|SC_FL_ERROR)) {
/* No more data are expected at this stage */
se_have_no_more_data(sc->sedesc);
}
else if (!cur_read && else if (!cur_read &&
!(sc->flags & (SC_FL_WONT_READ|SC_FL_NEED_BUFF|SC_FL_NEED_ROOM)) && !(sc->flags & (SC_FL_WONT_READ|SC_FL_NEED_BUFF|SC_FL_NEED_ROOM)) &&
!(sc->flags & (SC_FL_EOS|SC_FL_ABRT_DONE))) { !(sc->flags & (SC_FL_EOS|SC_FL_ABRT_DONE))) {
/* Subscribe to receive events if we're blocking on I/O */ /* Subscribe to receive events if we're blocking on I/O. Nothing
* was received and it was not because of a blocking
* condition.
*/
conn->mux->subscribe(sc, SUB_RETRY_RECV, &sc->wait_event); conn->mux->subscribe(sc, SUB_RETRY_RECV, &sc->wait_event);
se_have_no_more_data(sc->sedesc); se_have_no_more_data(sc->sedesc);
} }
else if (sc->flags & SC_FL_EOI) {
/* No more data are expected at this stage */
se_have_no_more_data(sc->sedesc);
}
else { else {
/* The mux may have more data to deliver. Be sure to be able to
* ask it ASAP
*/
se_have_more_data(sc->sedesc); se_have_more_data(sc->sedesc);
ret = 1; ret = 1;
} }