quic: Use GRO for reading packets from the UDP socket in upstream QUIC

This behavior is guarded by the runtime flag
`envoy.reloadable_features.prefer_udp_gro`.

We previously turned off GRO in `EnvoyQuicClientConnection` because we
weren't sure about the performance (see
envoyproxy#19088). However, kernel experts
have recommended using GRO over recvmmsg as a much more CPU efficient
solution for reading multiple UDP packets into a single buffer.

Signed-off-by: Ali Beyad <abeyad@google.com>

changelogs/current.yaml

@@ -47,6 +47,12 @@ minor_behavior_changes:
   change: |
     Enable obsolete line folding in BalsaParser (for behavior parity with http-parser, the
     previously used HTTP/1 parser).
+- area: http3
+  change: |
+    Use GRO (Generic Receive Offload) for reading packets from a UDP socket. See
+    https://www.kernel.org/doc/html/next/networking/segmentation-offloads.html for a description of
+    GRO. This behavior change can be reverted by setting
+    ``envoy.reloadable_features.prefer_udp_gro`` to ``false``.
 
 bug_fixes:
 # *Changes expected to improve the state of the world and are unlikely to have negative effects*

source/common/quic/envoy_quic_client_connection.cc

@@ -7,6 +7,7 @@
 #include "source/common/network/socket_option_factory.h"
 #include "source/common/network/udp_packet_writer_handler_impl.h"
 #include "source/common/quic/envoy_quic_utils.h"
+#include "source/common/runtime/runtime_features.h"
 
 namespace Envoy {
 namespace Quic {
@@ -229,7 +230,9 @@ void EnvoyQuicClientConnection::onFileEvent(uint32_t events,
   if (connected() && (events & Event::FileReadyType::Read)) {
     Api::IoErrorPtr err = Network::Utility::readPacketsFromSocket(
         connection_socket.ioHandle(), *connection_socket.connectionInfoProvider().localAddress(),
-        *this, dispatcher_.timeSource(), /*prefer_gro=*/false, packets_dropped_);
+        *this, dispatcher_.timeSource(),
+        Runtime::runtimeFeatureEnabled("envoy.reloadable_features.prefer_udp_gro"),
+        packets_dropped_);
     if (err == nullptr) {
       // In the case where the path validation fails, the probing socket will be closed and its IO
       // events are no longer interesting.

source/common/runtime/runtime_features.cc

@@ -75,6 +75,7 @@ RUNTIME_GUARD(envoy_reloadable_features_oauth_make_token_cookie_httponly);
 RUNTIME_GUARD(envoy_reloadable_features_oauth_use_standard_max_age_value);
 RUNTIME_GUARD(envoy_reloadable_features_oauth_use_url_encoding);
 RUNTIME_GUARD(envoy_reloadable_features_original_dst_rely_on_idle_timeout);
+RUNTIME_GUARD(envoy_reloadable_features_prefer_udp_gro);
 RUNTIME_GUARD(envoy_reloadable_features_proxy_status_upstream_request_timeout);
 RUNTIME_GUARD(envoy_reloadable_features_quic_fix_filter_manager_uaf);
 // Ignore the automated "remove this flag" issue: we should keep this for 1 year. Confirm with