[PATCH 1 of 4] Switched to using posted next events after sendfile_max_chunk

[Maxim Dounin]

# HG changeset patch
# User Maxim Dounin <mdounin at mdounin.ru>
# Date 1633978533 -10800
#      Mon Oct 11 21:55:33 2021 +0300
# Node ID d175cd09ac9d2bab7f7226eac3bfce196a296cc0
# Parent  ae7c767aa491fa55d3168dfc028a22f43ac8cf89
Switched to using posted next events after sendfile_max_chunk.

Previously, 1 millisecond delay was used instead.  In certain edge cases
this might result in noticeable performance degradation though, notably on
Linux with typical CONFIG_HZ=250 (so 1ms delay becomes 4ms),
sendfile_max_chunk 2m, and link speed above 2.5 Gbps.

Using posted next events removes the artificial delay and makes processing
fast in all cases.

diff --git a/src/http/ngx_http_write_filter_module.c b/src/http/ngx_http_write_filter_module.c
--- a/src/http/ngx_http_write_filter_module.c
+++ b/src/http/ngx_http_write_filter_module.c
@@ -331,8 +331,7 @@ ngx_http_write_filter(ngx_http_request_t
         && c->write->ready
         && c->sent - sent >= limit - (off_t) (2 * ngx_pagesize))
     {
-        c->write->delayed = 1;
-        ngx_add_timer(c->write, 1);
+        ngx_post_event(c->write, &ngx_posted_next_events);
     }
 
     for (cl = r->out; cl && cl != chain; /* void */) {