[nginx] QUIC: always add ACK frame to the queue head.

[Roman Arutyunyan]

details:   https://hg.nginx.org/nginx/rev/d7dec2970161
branches:  
changeset: 9139:d7dec2970161
user:      Roman Arutyunyan <arut at nginx.com>
date:      Thu Aug 10 20:11:29 2023 +0400
description:
QUIC: always add ACK frame to the queue head.

Previously it was added to the tail as all other frames.  However, if the
amount of queued data is large, it could delay the delivery of ACK, which
could trigger frames retransmissions and slow down the connection.

diffstat:

 src/event/quic/ngx_event_quic_output.c |  3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diffs (14 lines):

diff -r a90f79792b5d -r d7dec2970161 src/event/quic/ngx_event_quic_output.c
--- a/src/event/quic/ngx_event_quic_output.c	Thu Jul 27 16:37:17 2023 +0400
+++ b/src/event/quic/ngx_event_quic_output.c	Thu Aug 10 20:11:29 2023 +0400
@@ -1174,8 +1174,9 @@ ngx_quic_send_ack(ngx_connection_t *c, n
     frame->u.ack.delay = ack_delay;
     frame->u.ack.range_count = ctx->nranges;
     frame->u.ack.first_range = ctx->first_range;
+    frame->len = ngx_quic_create_frame(NULL, frame);
 
-    ngx_quic_queue_frame(qc, frame);
+    ngx_queue_insert_head(&ctx->frames, &frame->queue);
 
     return NGX_OK;
 }