Hello, I would like to re-submit a previously-reported bug report patch with a slight modification, after a short discussion with Christopher Faulet on the topic.
The details and fix are in the patch below. Thanks, Cody --- >From ec6deea1b5d1b3b92dc87a2100231aab276574f3 Mon Sep 17 00:00:00 2001 From: Cody Ohlsen <[email protected]> Date: Fri, 27 Mar 2026 16:40:01 -0700 Subject: [PATCH] BUG/MEDIUM: mux-h1: Don't set MSG_MORE on bodyless responses forwarded to client When h1_snd_buf() inherits the CO_SFL_MSG_MORE flag from the upper layer, it unconditionally propagates it to H1C_F_CO_MSG_MORE, which eventually sets MSG_MORE on the sendmsg() call. For bodyless responses (HEAD, 204, 304), this causes the kernel to cork the TCP connection for ~200ms waiting for body data that will never be sent. With an H1 frontend and H2 backend, this adds ~200ms of latency to many or all bodyless responses. The 200ms corresponds to the kernel's tcp_cork_time default. H1 backends are less affected because h1_postparse_res_hdrs() sets HTX_FL_EOM during header parsing for bodyless responses, but H2 backends frequently deliver the end-of-stream signal in a separate scheduling round, leaving htx_expect_more() returning TRUE when headers are first forwarded. The fix guards H1C_F_CO_MSG_MORE so it is only set when the connection is a backend (H1C_F_IS_BACK) or the response is not bodyless (!H1S_F_BODYLESS_RESP). This ensures bodyless responses on the front connection are sent immediately without corking. This should be backported to all stable branches. Co-developed-by: Billy Campoli <[email protected]> Co-developed-by: Chandan Avdhut <[email protected]> --- src/mux_h1.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/src/mux_h1.c b/src/mux_h1.c index 6b7e2ad..10ec8b6 100644 --- a/src/mux_h1.c +++ b/src/mux_h1.c @@ -4768,8 +4768,14 @@ static size_t h1_snd_buf(struct stconn *sc, struct buffer *buf, size_t count, in /* Inherit some flags from the upper layer */ h1c->flags &= ~(H1C_F_CO_MSG_MORE|H1C_F_CO_STREAMER); - if (flags & CO_SFL_MSG_MORE) - h1c->flags |= H1C_F_CO_MSG_MORE; + if (flags & CO_SFL_MSG_MORE) { + /* Don't set H1C_F_CO_MSG_MORE when sending a bodyless response to client. + * We must do that if the response is not finished, regardless it a bodyless + * response, to be sure to send it ASAP. + */ + if ((h1c->flags & H1C_F_IS_BACK) || !(h1s->flags & H1S_F_BODYLESS_RESP)) + h1c->flags |= H1C_F_CO_MSG_MORE; + } if (flags & CO_SFL_STREAMER) h1c->flags |= H1C_F_CO_STREAMER; -- 2.52.0
