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BUG/MINOR: quic: Missing listener accept queue tasklet wakeups

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This bug was revealed by h2load tests run as follows:

      h2load -t 4 --npn-list h3 -c 64 -m 16 -n 16384  -v https://127.0.0.1:4443/

This open (-c) 64 QUIC connections (-n) 16384 h3 requets from (-t) 4 threads, i.e.
256 requests by connection. Such tests could not always pass and often ended with
such results displays by h2load:

finished in 53.74s, 38.11 req/s, 493.78KB/s
requests: 16384 total, 2944 started, 2048 done, 2048 succeeded, 14336
failed, 14336 errored, 0 timeout
status codes: 2048 2xx, 0 3xx, 0 4xx, 0 5xx
traffic: 25.92MB (27174537) total, 102.00KB (104448) headers (space
savings 1.92%), 25.80MB (27053569) data
UDP datagram: 3883 sent, 24330 received
                     min         max         mean         sd         sd
time for request:    48.75ms    502.86ms    134.12ms     75.80ms    92.68%
time for connect:    20.94ms    331.24ms    189.59ms     84.81ms    59.38%
time to 1st byte:   394.36ms    417.01ms    406.72ms      9.14ms    75.00%
req/s           :       0.00      115.45       14.30       38.13    87.50%

The number of successful requests was always a multiple of 256.
Activating the traces also shew that some connections were blocked after having
successfully completed their handshakes due to the fact that the mux. The mux
is started upon the acceptation of the connection.

Under heavy load, some connections were never accepted. From the moment where
more than 4 (MAXACCEPT) connections were enqueued before a listener could be
woken up to accept at most 4 connections, the remaining connections were not
accepted ore lately at the second listener tasklet  wakeup.

Add a call to tasklet_wakeup() to the accept list tasklet of the listeners to
wake up it if there are remaining connections to accept after having called
listener_accept(). In this case the listener must not be removed of this
accept list, if not at the next call it will not accept anything more.

Must be backported to 2.7 and 2.6.

(cherry picked from commit 4377dbd756efa1645106b0e53d3ddaba9a6f0702)
Signed-off-by: Willy Tarreau <w@1wt.eu>
(cherry picked from commit 9cc091cb29114d71a30e703aa895a6fa9658336b)
Signed-off-by: Willy Tarreau <w@1wt.eu>
This commit is contained in:
Frdric Lcaille 2023-03-10 13:34:30 +01:00 committed by Willy Tarreau
parent 8104f11eaf
commit 2b6d33435e
1 changed files with 4 additions and 1 deletions
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5
src/quic_sock.c
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@ -542,7 +542,10 @@ static struct task *quic_accept_run(struct task *t, void *ctx, unsigned int i)
mt_list_for_each_entry_safe(lthr, &queue->listeners, quic_accept.list, elt1, elt2) {
listener_accept(lthr->li);
MT_LIST_DELETE_SAFE(elt1);
if (!MT_LIST_ISEMPTY(&lthr->quic_accept.conns))
tasklet_wakeup((struct tasklet*)t);
else
MT_LIST_DELETE_SAFE(elt1);
}
return NULL;