Merge pull request #14943 from grpc/revert-14688-revert_pr

Revert "Revert "Use heuristic to determine how many events to handle per iter…"

src/core/lib/iomgr/ev_epollex_linux.cc

@@ -59,7 +59,10 @@
 //#define GRPC_EPOLLEX_CREATE_WORKERS_ON_HEAP 1
 
 #define MAX_EPOLL_EVENTS 100
-#define MAX_EPOLL_EVENTS_HANDLED_EACH_POLL_CALL 1
+// TODO(juanlishen): We use a greater-than-one value here as a workaround fix to
+// a keepalive ping timeout issue. We may want to revert https://github
+// .com/grpc/grpc/pull/14943 once we figure out the root cause.
+#define MAX_EPOLL_EVENTS_HANDLED_EACH_POLL_CALL 16
 
 grpc_core::DebugOnlyTraceFlag grpc_trace_pollable_refcount(false,
                                                            "pollable_refcount");
@@ -198,6 +201,7 @@ struct grpc_pollset_worker {
 
 struct grpc_pollset {
   gpr_mu mu;
+  gpr_atm worker_count;
   pollable* active_pollable;
   bool kicked_without_poller;
   grpc_closure* shutdown_closure;
@@ -685,6 +689,7 @@ static grpc_error* pollset_kick_all(grpc_pollset* pollset) {
 
 static void pollset_init(grpc_pollset* pollset, gpr_mu** mu) {
   gpr_mu_init(&pollset->mu);
+  gpr_atm_no_barrier_store(&pollset->worker_count, 0);
   pollset->active_pollable = POLLABLE_REF(g_empty_pollable, "pollset");
   pollset->kicked_without_poller = false;
   pollset->shutdown_closure = nullptr;
@@ -758,8 +763,20 @@ static grpc_error* pollable_process_events(grpc_pollset* pollset,
                                            pollable* pollable_obj, bool drain) {
   GPR_TIMER_SCOPE("pollable_process_events", 0);
   static const char* err_desc = "pollset_process_events";
+  // Use a simple heuristic to determine how many fd events to process
+  // per loop iteration.  (events/workers)
+  int handle_count = 1;
+  int worker_count = gpr_atm_no_barrier_load(&pollset->worker_count);
+  GPR_ASSERT(worker_count > 0);
+  handle_count =
+      (pollable_obj->event_count - pollable_obj->event_cursor) / worker_count;
+  if (handle_count == 0) {
+    handle_count = 1;
+  } else if (handle_count > MAX_EPOLL_EVENTS_HANDLED_EACH_POLL_CALL) {
+    handle_count = MAX_EPOLL_EVENTS_HANDLED_EACH_POLL_CALL;
+  }
   grpc_error* error = GRPC_ERROR_NONE;
-  for (int i = 0; (drain || i < MAX_EPOLL_EVENTS_HANDLED_EACH_POLL_CALL) &&
+  for (int i = 0; (drain || i < handle_count) &&
                   pollable_obj->event_cursor != pollable_obj->event_count;
        i++) {
     int n = pollable_obj->event_cursor++;
@@ -884,6 +901,7 @@ static bool begin_worker(grpc_pollset* pollset, grpc_pollset_worker* worker,
   GPR_TIMER_SCOPE("begin_worker", 0);
   bool do_poll =
       (pollset->shutdown_closure == nullptr && !pollset->already_shutdown);
+  gpr_atm_no_barrier_fetch_add(&pollset->worker_count, 1);
   if (worker_hdl != nullptr) *worker_hdl = worker;
   worker->initialized_cv = false;
   worker->kicked = false;
@@ -964,6 +982,7 @@ static void end_worker(grpc_pollset* pollset, grpc_pollset_worker* worker,
   if (worker->initialized_cv) {
     gpr_cv_destroy(&worker->cv);
   }
+  gpr_atm_no_barrier_fetch_add(&pollset->worker_count, -1);
 }
 
 #ifndef NDEBUG