Trace statements in epoll poller (enabled by default to debug the recent

perf regression)

src/core/lib/iomgr/ev_epoll_linux.c

@@ -60,6 +60,14 @@
 #include "src/core/lib/profiling/timers.h"
 #include "src/core/lib/support/block_annotate.h"
 
+/* TODO: sreek - Move this to init.c and initialize this like other tracers.
+ * Also, enable this trace by default for now. */
+static int grpc_polling_trace = 1;
+#define GRPC_POLLING_TRACE(fmt, ...)       \
+  if (grpc_polling_trace) {                \
+    gpr_log(GPR_INFO, (fmt), __VA_ARGS__); \
+  }
+
 static int grpc_wakeup_signal = -1;
 static bool is_grpc_wakeup_signal_initialized = false;
 
@@ -1058,6 +1066,8 @@ static void pollset_global_shutdown(void) {
 
 static grpc_error *pollset_worker_kick(grpc_pollset_worker *worker) {
   grpc_error *err = GRPC_ERROR_NONE;
+  GRPC_POLLING_TRACE("pollset_worker_kick: Kicking worker: %p (thread id: %ld)",
+                     (void *)worker, worker->pt_id);
   int err_num = pthread_kill(worker->pt_id, grpc_wakeup_signal);
   if (err_num != 0) {
     err = GRPC_OS_ERROR(err_num, "pthread_kill");
@@ -1104,7 +1114,6 @@ static grpc_error *pollset_kick(grpc_pollset *p,
   GPR_TIMER_BEGIN("pollset_kick", 0);
   grpc_error *error = GRPC_ERROR_NONE;
   const char *err_desc = "Kick Failure";
-
   grpc_pollset_worker *worker = specific_worker;
   if (worker != NULL) {
     if (worker == GRPC_POLLSET_KICK_BROADCAST) {
@@ -1270,7 +1279,8 @@ static void pollset_reset(grpc_pollset *pollset) {
 #define GRPC_EPOLL_MAX_EVENTS 1000
 /* Note: sig_mask contains the signal mask to use *during* epoll_wait() */
 static void pollset_work_and_unlock(grpc_exec_ctx *exec_ctx,
-                                    grpc_pollset *pollset, int timeout_ms,
+                                    grpc_pollset *pollset,
+                                    grpc_pollset_worker *worker, int timeout_ms,
                                     sigset_t *sig_mask, grpc_error **error) {
   struct epoll_event ep_ev[GRPC_EPOLL_MAX_EVENTS];
   int epoll_fd = -1;
@@ -1298,6 +1308,8 @@ static void pollset_work_and_unlock(grpc_exec_ctx *exec_ctx,
     }
 
     PI_ADD_REF(pollset->polling_island, "ps");
+    GRPC_POLLING_TRACE("pollset_work: pollset: %p created new pi: %p",
+                       (void *)pollset, (void *)pollset->polling_island);
   }
 
   pi = polling_island_maybe_get_latest(pollset->polling_island);
@@ -1331,6 +1343,9 @@ static void pollset_work_and_unlock(grpc_exec_ctx *exec_ctx,
       } else {
         /* We were interrupted. Save an interation by doing a zero timeout
            epoll_wait to see if there are any other events of interest */
+        GRPC_POLLING_TRACE(
+            "pollset_work: pollset: %p, worker: %p received kick",
+            (void *)pollset, (void *)worker);
         ep_rv = epoll_wait(epoll_fd, ep_ev, GRPC_EPOLL_MAX_EVENTS, 0);
       }
     }
@@ -1347,6 +1362,10 @@ static void pollset_work_and_unlock(grpc_exec_ctx *exec_ctx,
                      grpc_wakeup_fd_consume_wakeup(&grpc_global_wakeup_fd),
                      err_desc);
       } else if (data_ptr == &polling_island_wakeup_fd) {
+        GRPC_POLLING_TRACE(
+            "pollset_work: pollset: %p, worker: %p polling island (epoll_fd: "
+            "%d) got merged",
+            (void *)pollset, (void *)worker, epoll_fd);
         /* This means that our polling island is merged with a different
            island. We do not have to do anything here since the subsequent call
            to the function pollset_work_and_unlock() will pick up the correct
@@ -1442,8 +1461,8 @@ static grpc_error *pollset_work(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
 
     push_front_worker(pollset, &worker); /* Add worker to pollset */
 
-    pollset_work_and_unlock(exec_ctx, pollset, timeout_ms, &g_orig_sigmask,
-                            &error);
+    pollset_work_and_unlock(exec_ctx, pollset, &worker, timeout_ms,
+                            &g_orig_sigmask, &error);
     grpc_exec_ctx_flush(exec_ctx);
 
     gpr_mu_lock(&pollset->mu);
@@ -1506,17 +1525,38 @@ static void pollset_add_fd(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
     pi_new = fd->polling_island;
     if (pi_new == NULL) {
       pi_new = polling_island_create(fd, &error);
+
+      GRPC_POLLING_TRACE(
+          "pollset_add_fd: Created new polling island. pi_new:%p (fd: %d, "
+          "pollset: %p)",
+          (void *)pi_new, fd->fd, (void *)pollset);
     }
   } else if (fd->polling_island == NULL) {
     pi_new = polling_island_lock(pollset->polling_island);
     polling_island_add_fds_locked(pi_new, &fd, 1, true, &error);
     gpr_mu_unlock(&pi_new->mu);
+
+    GRPC_POLLING_TRACE(
+        "pollset_add_fd: fd->pi was NULL. pi_new: %p (fd: %d, pollset: %p, "
+        "pollset->pi: %p)",
+        (void *)pi_new, fd->fd, (void *)pollset,
+        (void *)pollset->polling_island);
   } else if (pollset->polling_island == NULL) {
     pi_new = polling_island_lock(fd->polling_island);
     gpr_mu_unlock(&pi_new->mu);
+
+    GRPC_POLLING_TRACE(
+        "pollset_add_fd: pollset->pi was NULL. pi_new: %p (fd: %d, pollset: "
+        "%p, fd->pi: %p",
+        (void *)pi_new, fd->fd, (void *)pollset, (void *)fd->polling_island);
   } else {
     pi_new = polling_island_merge(fd->polling_island, pollset->polling_island,
                                   &error);
+    GRPC_POLLING_TRACE(
+        "pollset_add_fd: polling islands merged. pi_new: %p (fd: %d, pollset: "
+        "%p, fd->pi: %p, pollset->pi: %p)",
+        (void *)pi_new, fd->fd, (void *)pollset, (void *)fd->polling_island,
+        (void *)pollset->polling_island);
   }
 
   /* At this point, pi_new is the polling island that both fd->polling_island