Context

Based on this discussion, we are seeing that libevent is using polling on iOS instead of kqueue.

This is extremely unperformant, and is causing Envoy Mobile to use ~100% CPU on iOS devices.

To validate that this was the root cause, we were able to hardcode an entry in this file to force kqueue to be enabled:

"EVENT__HAVE_WORKING_KQUEUE": "on"

After building, we could verify that the expected conditional was defined:

mrebello-mbp151:envoy-mobile mrebello$ cat ./bazel-out/ios-x86_64-min10.0-applebin_ios-ios_x86_64-fastbuild/bin/external/envoy/bazel/foreign_cc/event/include/event2/event-config.h|grep WORKING
#define EVENT__HAVE_WORKING_KQUEUE 1

When running Envoy on a device, CPU went from ~100% to just 1.5% with this change.

Task

Apply an upstream fix that enables kqueue on Apple/iOS platforms so that we can fix this performance issue on iOS.