MINOR: mux-quic: use sched call time for pacing

QUIC pacing was recently implemented to limit burst and improve overall
bandwidth. This is used only for MUX STREAM emission. Pacing requires
nanosecond resolution. As such, it used now_cpu_time() which relies on
clock_gettime() syscall.

The usage of clock_gettime() has several drawbacks :
* it is a syscall and thus requires a context-switch which may hurt
  performance
* it is not be available on all systems
* timestamp is retrieved multiple times during a single task execution,
  thus yielding different values which may tamper pacing calculation

Improve this by using task_mono_time() instead. This returns task call
time from the scheduler thread context. It requires the flag
TASK_F_WANTS_TIME on QUIC MUX tasklet to force the scheduler to update
call time with now_mono_time(). This solves every limitations listed
above :
* syscall invokation is only performed once before tasklet execution,
  thus reducing context-switch impact
* on non compatible system, a millisecond timer is used as a fallback
  which should ensure that pacing works decently for them
* timer value is now guaranteed to be fixed duing task execution

diff --git a/include/haproxy/mux_quic-t.h b/include/haproxy/mux_quic-t.h
index a0f8e0dbdf5503e0b83cb9347cb049658e90dc30..2fd3edab86fef166427d8adc3ceb18c2309cbfb2 100644 (file)
--- a/include/haproxy/mux_quic-t.h
+++ b/include/haproxy/mux_quic-t.h
@@ -18,6 +18,7 @@
 #include <haproxy/quic_pacing-t.h>
 #include <haproxy/quic_stream-t.h>
 #include <haproxy/stconn-t.h>
+#include <haproxy/task-t.h>
 #include <haproxy/time-t.h>
 
 /* Stream types */

diff --git a/src/mux_quic.c b/src/mux_quic.c
index 03a7b293820ec0739f07849e38ba09d91a8122f9..64e6df2113121f7c4e4ca491f2c0f340fa41e41f 100644 (file)
--- a/src/mux_quic.c
+++ b/src/mux_quic.c
@@ -2996,6 +2996,7 @@ static int qmux_init(struct connection *conn, struct proxy *prx,
 
        qcc->wait_event.tasklet->process = qcc_io_cb;
        qcc->wait_event.tasklet->context = qcc;
+       qcc->wait_event.tasklet->state  |= TASK_F_WANTS_TIME;
        qcc->wait_event.events = 0;
 
        qcc->proxy = prx;

diff --git a/src/quic_pacing.c b/src/quic_pacing.c
index 7b1e5b9dc195eadb2e3bd2ebbe009eb362960dea..9dfa35206227ffceaeda230096db57db4f67748c 100644 (file)
--- a/src/quic_pacing.c
+++ b/src/quic_pacing.c
@@ -1,16 +1,17 @@
 #include <haproxy/quic_pacing.h>
 
 #include <haproxy/quic_tx.h>
+#include <haproxy/task.h>
 
 /* Returns true if <pacer> timer is expired and emission can be retried. */
 int quic_pacing_expired(const struct quic_pacer *pacer)
 {
-       return !pacer->next || pacer->next <= now_mono_time();
+       return !pacer->next || pacer->next <= task_mono_time();
 }
 
 /* Notify <pacer> about an emission of <sent> count of datagrams. */
 void quic_pacing_sent_done(struct quic_pacer *pacer, int sent)
 {
-       pacer->next = now_mono_time() + pacer->cc->algo->pacing_rate(pacer->cc) * sent;
+       pacer->next = task_mono_time() + pacer->cc->algo->pacing_rate(pacer->cc) * sent;
        pacer->last_sent = sent;
 }