[PATCH 2 of 4] QUIC: always add ACK frame to the queue head

[Vladimir Homutov]

On Thu, Aug 10, 2023 at 08:02:06PM +0400, Sergey Kandaurov wrote:
>
> > On 27 Jul 2023, at 16:42, Roman Arutyunyan <arut at nginx.com> wrote:
> >
> > # HG changeset patch
> > # User Roman Arutyunyan <arut at nginx.com>
> > # Date 1690461509 -14400
> > #      Thu Jul 27 16:38:29 2023 +0400
> > # Node ID 0d12ada84c168c62e9bae847af2725641da583d0
> > # Parent  2fd16fc76920ef0b8ea2fa64858934e38c4477c5
> > 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.
> >
> > diff --git a/src/event/quic/ngx_event_quic_output.c b/src/event/quic/ngx_event_quic_output.c
> > --- a/src/event/quic/ngx_event_quic_output.c
> > +++ b/src/event/quic/ngx_event_quic_output.c
> > @@ -1175,7 +1175,9 @@ ngx_quic_send_ack(ngx_connection_t *c, n
> >     frame->u.ack.range_count = ctx->nranges;
> >     frame->u.ack.first_range = ctx->first_range;
> >
> > -    ngx_quic_queue_frame(qc, frame);
> > +    ngx_queue_insert_head(&ctx->frames, &frame->queue);
> > +
> > +    frame->len = ngx_quic_create_frame(NULL, frame);
> >
> >     return NGX_OK;
> > }
>
> place frame->len first, to other frame assignments?
>
> Otherwise, looks good.

The ngx_quic_queue_frame() functions also posts the push event.

Most likely it will be set anyway, but formally the change missing it.