Merge pull request #13435 from sreecha/disable-realtime-caching

Disable caching start-time for all clock-types except GPR_CLOCK_MONOTONIC

src/core/lib/iomgr/exec_ctx.cc

@@ -25,9 +25,6 @@
 #include "src/core/lib/iomgr/combiner.h"
 #include "src/core/lib/profiling/timers.h"
 
-#define GRPC_START_TIME_UPDATE_INTERVAL 10000
-extern "C" grpc_tracer_flag grpc_timer_check_trace;
-
 bool grpc_exec_ctx_ready_to_finish(grpc_exec_ctx* exec_ctx) {
   if ((exec_ctx->flags & GRPC_EXEC_CTX_FLAG_IS_FINISHED) == 0) {
     if (exec_ctx->check_ready_to_finish(exec_ctx,
@@ -107,49 +104,16 @@ static void exec_ctx_sched(grpc_exec_ctx* exec_ctx, grpc_closure* closure,
   grpc_closure_list_append(&exec_ctx->closure_list, closure, error);
 }
 
-/* This time pair is not entirely thread-safe as store/load of tv_sec and
- * tv_nsec are performed separately. However g_start_time do not need to have
- * sub-second precision, so it is ok if the value of tv_nsec is off in this
- * case. */
-typedef struct time_atm_pair {
-  gpr_atm tv_sec;
-  gpr_atm tv_nsec;
-} time_atm_pair;
-
-static time_atm_pair
-    g_start_time[GPR_TIMESPAN + 1];  // assumes GPR_TIMESPAN is the
-                                     // last enum value in
-                                     // gpr_clock_type
-static grpc_millis g_last_start_time_update;
-
-static gpr_timespec timespec_from_time_atm_pair(const time_atm_pair* src,
-                                                gpr_clock_type clock_type) {
-  gpr_timespec time;
-  time.tv_nsec = (int32_t)gpr_atm_no_barrier_load(&src->tv_nsec);
-  time.tv_sec = (int64_t)gpr_atm_no_barrier_load(&src->tv_sec);
-  time.clock_type = clock_type;
-  return time;
-}
-
-static void time_atm_pair_store(time_atm_pair* dst, const gpr_timespec src) {
-  gpr_atm_no_barrier_store(&dst->tv_sec, src.tv_sec);
-  gpr_atm_no_barrier_store(&dst->tv_nsec, src.tv_nsec);
-}
+static gpr_timespec g_start_time;
 
 void grpc_exec_ctx_global_init(void) {
-  for (int i = 0; i < GPR_TIMESPAN; i++) {
-    time_atm_pair_store(&g_start_time[i], gpr_now((gpr_clock_type)i));
-  }
-  // allows uniform treatment in conversion functions
-  time_atm_pair_store(&g_start_time[GPR_TIMESPAN], gpr_time_0(GPR_TIMESPAN));
+  g_start_time = gpr_now(GPR_CLOCK_MONOTONIC);
 }
 
 void grpc_exec_ctx_global_shutdown(void) {}
 
 static gpr_atm timespec_to_atm_round_down(gpr_timespec ts) {
-  gpr_timespec start_time =
-      timespec_from_time_atm_pair(&g_start_time[ts.clock_type], ts.clock_type);
-  ts = gpr_time_sub(ts, start_time);
+  ts = gpr_time_sub(ts, g_start_time);
   double x =
       GPR_MS_PER_SEC * (double)ts.tv_sec + (double)ts.tv_nsec / GPR_NS_PER_MS;
   if (x < 0) return 0;
@@ -158,9 +122,7 @@ static gpr_atm timespec_to_atm_round_down(gpr_timespec ts) {
 }
 
 static gpr_atm timespec_to_atm_round_up(gpr_timespec ts) {
-  gpr_timespec start_time =
-      timespec_from_time_atm_pair(&g_start_time[ts.clock_type], ts.clock_type);
-  ts = gpr_time_sub(ts, start_time);
+  ts = gpr_time_sub(ts, g_start_time);
   double x = GPR_MS_PER_SEC * (double)ts.tv_sec +
              (double)ts.tv_nsec / GPR_NS_PER_MS +
              (double)(GPR_NS_PER_SEC - 1) / (double)GPR_NS_PER_SEC;
@@ -195,41 +157,18 @@ gpr_timespec grpc_millis_to_timespec(grpc_millis millis,
   if (clock_type == GPR_TIMESPAN) {
     return gpr_time_from_millis(millis, GPR_TIMESPAN);
   }
-  gpr_timespec start_time =
-      timespec_from_time_atm_pair(&g_start_time[clock_type], clock_type);
-  return gpr_time_add(start_time, gpr_time_from_millis(millis, GPR_TIMESPAN));
+  return gpr_time_add(gpr_convert_clock_type(g_start_time, clock_type),
+                      gpr_time_from_millis(millis, GPR_TIMESPAN));
 }
 
 grpc_millis grpc_timespec_to_millis_round_down(gpr_timespec ts) {
-  return timespec_to_atm_round_down(ts);
+  return timespec_to_atm_round_down(
+      gpr_convert_clock_type(ts, g_start_time.clock_type));
 }
 
 grpc_millis grpc_timespec_to_millis_round_up(gpr_timespec ts) {
-  return timespec_to_atm_round_up(ts);
-}
-
-void grpc_exec_ctx_maybe_update_start_time(grpc_exec_ctx* exec_ctx) {
-  grpc_millis now = grpc_exec_ctx_now(exec_ctx);
-  grpc_millis last_start_time_update =
-      gpr_atm_no_barrier_load(&g_last_start_time_update);
-
-  if (now > last_start_time_update &&
-      now - last_start_time_update > GRPC_START_TIME_UPDATE_INTERVAL) {
-    /* Get the current system time and subtract \a now from it, where \a now is
-     * the relative time from grpc_init() from monotonic clock. This calibrates
-     * the time when grpc_exec_ctx_global_init was called based on current
-     * system clock. */
-    gpr_atm_no_barrier_store(&g_last_start_time_update, now);
-    gpr_timespec real_now = gpr_now(GPR_CLOCK_REALTIME);
-    gpr_timespec real_start_time =
-        gpr_time_sub(real_now, gpr_time_from_millis(now, GPR_TIMESPAN));
-    time_atm_pair_store(&g_start_time[GPR_CLOCK_REALTIME], real_start_time);
-
-    if (GRPC_TRACER_ON(grpc_timer_check_trace)) {
-      gpr_log(GPR_DEBUG, "Update realtime clock start time: %" PRId64 "s %dns",
-              real_start_time.tv_sec, real_start_time.tv_nsec);
-    }
-  }
+  return timespec_to_atm_round_up(
+      gpr_convert_clock_type(ts, g_start_time.clock_type));
 }
 
 static const grpc_closure_scheduler_vtable exec_ctx_scheduler_vtable = {

src/core/lib/iomgr/exec_ctx.h

@@ -124,8 +124,6 @@ gpr_timespec grpc_millis_to_timespec(grpc_millis millis, gpr_clock_type clock);
 grpc_millis grpc_timespec_to_millis_round_down(gpr_timespec timespec);
 grpc_millis grpc_timespec_to_millis_round_up(gpr_timespec timespec);
 
-void grpc_exec_ctx_maybe_update_start_time(grpc_exec_ctx* exec_ctx);
-
 #ifdef __cplusplus
 }
 #endif

src/core/lib/iomgr/timer_manager.cc

@@ -226,10 +226,6 @@ static void timer_main_loop(grpc_exec_ctx* exec_ctx) {
     grpc_millis next = GRPC_MILLIS_INF_FUTURE;
     grpc_exec_ctx_invalidate_now(exec_ctx);
 
-    /* Calibrate g_start_time in exec_ctx.cc with a regular interval in case the
-     * system clock has changed */
-    grpc_exec_ctx_maybe_update_start_time(exec_ctx);
-
     // check timer state, updates next to the next time to run a check
     switch (grpc_timer_check(exec_ctx, &next)) {
       case GRPC_TIMERS_FIRED: