MINOR: quic: activate UDP GSO for QUIC if supported

Add a startup test for GSO support in quic_test_socketopts() and
automatically activate it in qc_prep_pkts() when building datagrams as
big as MTU.

Also define a new config option tune.quic.disable-udp-gso. This is
useful to prevent warning on older platform or to debug an issue which
may be related to GSO.

doc/configuration.txt

@@ -1414,6 +1414,7 @@ The following keywords are supported in the "global" section :
    - tune.pool-low-fd-ratio
    - tune.pt.zero-copy-forwarding
    - tune.quic.cc-hystart
+   - tune.quic.disable-udp-gso
    - tune.quic.frontend.conn-tx-buffers.limit
    - tune.quic.frontend.glitches-threshold
    - tune.quic.frontend.max-idle-timeout
@@ -3770,6 +3771,12 @@ tune.quic.cc-hystart { on | off }
   QUIC connections used as a replacement for the slow start phase of congestion
   control algorithms which may cause high packet loss. It is disabled by default.
 
+tune.quic.disable-udp-gso
+  Disable UDP GSO emission. This kernel feature allows to emit multiple
+  datagrams via a single system call which is more efficient for large
+  transfer. It may be useful to disable it on developers suggestion when
+  suspecting an issue on emission.
+
 tune.quic.frontend.conn-tx-buffers.limit <number>
   This settings defines the maximum number of buffers allocated for a QUIC
   connection on data emission. By default, it is set to 30. QUIC buffers are

include/haproxy/global-t.h

@@ -85,6 +85,7 @@
 #define GTUNE_LISTENER_MQ_OPT    (1<<28)
 #define GTUNE_LISTENER_MQ_ANY    (GTUNE_LISTENER_MQ_FAIR | GTUNE_LISTENER_MQ_OPT)
 #define GTUNE_QUIC_CC_HYSTART    (1<<29)
+#define GTUNE_QUIC_NO_UDP_GSO    (1<<30)
 
 #define NO_ZERO_COPY_FWD             0x0001 /* Globally disable zero-copy FF */
 #define NO_ZERO_COPY_FWD_PT          0x0002 /* disable zero-copy FF for PT (recv & send are disabled automatically) */

src/cfgparse-quic.c

@@ -1,5 +1,6 @@
 #include <errno.h>
 #include <string.h>
+#include <netinet/udp.h>
 
 #include <haproxy/api.h>
 #include <haproxy/cfgparse.h>
@@ -259,6 +260,29 @@ static int cfg_parse_quic_tune_setting(char **args, int section_type,
 	return 0;
 }
 
+static int cfg_parse_quic_tune_setting0(char **args, int section_type,
+                                        struct proxy *curpx,
+                                        const struct proxy *defpx,
+                                        const char *file, int line, char **err)
+{
+	int prefix_len = strlen("tune.quic.");
+	const char *suffix;
+
+	if (too_many_args(0, args, err, NULL))
+		return -1;
+
+	suffix = args[0] + prefix_len;
+	if (strcmp(suffix, "disable-udp-gso") == 0) {
+		global.tune.options |= GTUNE_QUIC_NO_UDP_GSO;
+	}
+	else {
+		memprintf(err, "'%s' keyword unhandled (please report this bug).", args[0]);
+		return -1;
+	}
+
+	return 0;
+}
+
 /* config parser for global "tune.quic.* {on|off}" */
 static int cfg_parse_quic_tune_on_off(char **args, int section_type, struct proxy *curpx,
                                       const struct proxy *defpx, const char *file, int line,
@@ -308,6 +332,7 @@ static struct cfg_kw_list cfg_kws = {ILH, {
 	{ CFG_GLOBAL, "tune.quic.max-frame-loss", cfg_parse_quic_tune_setting },
 	{ CFG_GLOBAL, "tune.quic.reorder-ratio", cfg_parse_quic_tune_setting },
 	{ CFG_GLOBAL, "tune.quic.retry-threshold", cfg_parse_quic_tune_setting },
+	{ CFG_GLOBAL, "tune.quic.disable-udp-gso", cfg_parse_quic_tune_setting0 },
 	{ CFG_GLOBAL, "tune.quic.zero-copy-fwd-send", cfg_parse_quic_tune_on_off },
 	{ 0, NULL, NULL }
 }};

src/proto_quic.c

@@ -555,6 +555,28 @@ static int quic_test_socketopts(struct listener *l)
 #endif
 	}
 
+	/* Check for UDP GSO support. */
+	if (!(global.tune.options & GTUNE_QUIC_NO_UDP_GSO)) {
+		if (fdtest < 0) {
+			fdtest = socket(rx->proto->fam->sock_domain,
+					rx->proto->sock_type, rx->proto->sock_prot);
+			if (fdtest < 0)
+				goto err;
+		}
+
+#ifdef UDP_SEGMENT
+		if (setsockopt(fdtest, SOL_UDP, UDP_SEGMENT, &zero, sizeof(zero))) {
+			ha_alert("Your platform does not support UDP GSO. "
+			         "This will be automatically disabled for QUIC transfer.\n");
+			global.tune.options |= GTUNE_QUIC_NO_UDP_GSO;
+		}
+#else
+		ha_alert("Your platform does not support UDP GSO. "
+		         "This will be automatically disabled for QUIC transfer.\n");
+		global.tune.options |= GTUNE_QUIC_NO_UDP_GSO;
+#endif
+	}
+
 	close(fdtest);
 	return ERR_NONE;