Add hysteresis to avoid mallocs

src/core/lib/iomgr/tcp_posix.c

@@ -135,23 +135,34 @@ static void run_poller(grpc_exec_ctx *exec_ctx, void *bp,
     gpr_log(GPR_DEBUG, "BACKUP_POLLER:%p run", p);
   }
   gpr_mu_lock(p->pollset_mu);
+  gpr_timespec now = gpr_now(GPR_CLOCK_MONOTONIC);
+  gpr_timespec deadline =
+      gpr_time_add(now, gpr_time_from_seconds(10, GPR_TIMESPAN));
   GRPC_LOG_IF_ERROR("backup_poller:pollset_work",
                     grpc_pollset_work(exec_ctx, BACKUP_POLLER_POLLSET(p), NULL,
-                                      gpr_now(GPR_CLOCK_MONOTONIC),
-                                      gpr_inf_future(GPR_CLOCK_MONOTONIC)));
+                                      now, deadline));
   gpr_mu_unlock(p->pollset_mu);
-  if (gpr_atm_no_barrier_load(&g_backup_poller) == (gpr_atm)p) {
+  /* last "uncovered" notification is the ref that keeps us polling, if we get
+   * there try a cas to release it */
+  if (gpr_atm_no_barrier_load(&g_uncovered_notifications_pending) == 1 &&
+      gpr_atm_full_cas(&g_uncovered_notifications_pending, 1, 0)) {
+    gpr_mu_lock(p->pollset_mu);
+    bool cas_ok = gpr_atm_no_barrier_cas(&g_backup_poller, (gpr_atm)p, 0);
     if (GRPC_TRACER_ON(grpc_tcp_trace)) {
-      gpr_log(GPR_DEBUG, "BACKUP_POLLER:%p reschedule", p);
+      gpr_log(GPR_DEBUG, "BACKUP_POLLER:%p done cas_ok=%d", p, cas_ok);
     }
-    GRPC_CLOSURE_SCHED(exec_ctx, &p->run_poller, GRPC_ERROR_NONE);
-  } else {
+    gpr_mu_unlock(p->pollset_mu);
     if (GRPC_TRACER_ON(grpc_tcp_trace)) {
       gpr_log(GPR_DEBUG, "BACKUP_POLLER:%p shutdown", p);
     }
     grpc_pollset_shutdown(exec_ctx, BACKUP_POLLER_POLLSET(p),
                           GRPC_CLOSURE_INIT(&p->run_poller, done_poller, p,
                                             grpc_schedule_on_exec_ctx));
+  } else {
+    if (GRPC_TRACER_ON(grpc_tcp_trace)) {
+      gpr_log(GPR_DEBUG, "BACKUP_POLLER:%p reschedule", p);
+    }
+    GRPC_CLOSURE_SCHED(exec_ctx, &p->run_poller, GRPC_ERROR_NONE);
   }
 }
 
@@ -163,16 +174,7 @@ static void drop_uncovered(grpc_exec_ctx *exec_ctx, grpc_tcp *tcp) {
     gpr_log(GPR_DEBUG, "BACKUP_POLLER:%p uncover cnt %d->%d", p, (int)old_count,
             (int)old_count - 1);
   }
-  if (old_count == 1) {
-    gpr_mu_lock(p->pollset_mu);
-    bool cas_ok = gpr_atm_no_barrier_cas(&g_backup_poller, (gpr_atm)p, 0);
-    if (GRPC_TRACER_ON(grpc_tcp_trace)) {
-      gpr_log(GPR_DEBUG, "BACKUP_POLLER:%p done cas_ok=%d", p, cas_ok);
-    }
-    GRPC_LOG_IF_ERROR("backup_poller:pollset_kick",
-                      grpc_pollset_kick(BACKUP_POLLER_POLLSET(p), NULL));
-    gpr_mu_unlock(p->pollset_mu);
-  }
+  GPR_ASSERT(old_count != 1);
 }
 
 static void cover_self(grpc_exec_ctx *exec_ctx, grpc_tcp *tcp) {
@@ -203,7 +205,9 @@ static void cover_self(grpc_exec_ctx *exec_ctx, grpc_tcp *tcp) {
     gpr_log(GPR_DEBUG, "BACKUP_POLLER:%p add %p", p, tcp);
   }
   grpc_pollset_add_fd(exec_ctx, BACKUP_POLLER_POLLSET(p), tcp->em_fd);
-  drop_uncovered(exec_ctx, tcp);
+  if (old_count != 0) {
+    drop_uncovered(exec_ctx, tcp);
+  }
 }
 
 static void notify_on_read(grpc_exec_ctx *exec_ctx, grpc_tcp *tcp) {