MINOR: listener: refine the default MAX_ACCEPT from 64 to 4
The maximum number of connections accepted at once by a thread for a single
listener used to default to 64 divided by the number of processes but the
tasklet-based model is much more scalable and benefits from smaller values.
Experimentation has shown that 4 gives the highest accept rate for all
thread values, and that 3 and 5 come very close, as shown below (HTTP/1
connections forwarded per second at multi-accept 4 and 64):
ac\thr| 1 2 4 8 16
------+------------------------------
4| 80k 106k 168k 270k 336k
64| 63k 89k 145k 230k 274k
Some tests were also conducted on SSL and absolutely no change was observed.
The value was placed into a define because it used to be spread all over the
code.
It might be useful at some point to backport this to 2.3 and 2.2 to help
those who observed some performance regressions from 1.6.
diff --git a/src/listener.c b/src/listener.c
index 9ca910b..48ba8e0 100644
--- a/src/listener.c
+++ b/src/listener.c
@@ -131,7 +131,7 @@
/* if global.tune.maxaccept is -1, then max_accept is UINT_MAX. It
* is not really illimited, but it is probably enough.
*/
- max_accept = global.tune.maxaccept ? global.tune.maxaccept : 64;
+ max_accept = global.tune.maxaccept ? global.tune.maxaccept : MAX_ACCEPT;
for (; max_accept; max_accept--) {
conn = accept_queue_pop_sc(ring);
if (!conn)