From 7b84f81a8ca570c3d1e74bbb98d8d38de2bce3c7 Mon Sep 17 00:00:00 2001
From: Soheil Hassas Yeganeh <soheil@google.com>
Date: Tue, 13 Aug 2019 15:04:03 -0400
Subject: [PATCH] Add grpc_cycle_counter_to_millis().

---
 .../filters/client_channel/client_channel.cc    |  3 +--
 src/core/lib/iomgr/exec_ctx.cc                  | 17 +++++++++++++++++
 src/core/lib/iomgr/exec_ctx.h                   |  3 +++
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/src/core/ext/filters/client_channel/client_channel.cc b/src/core/ext/filters/client_channel/client_channel.cc
index 51210107872..0a9b5ac43fb 100644
--- a/src/core/ext/filters/client_channel/client_channel.cc
+++ b/src/core/ext/filters/client_channel/client_channel.cc
@@ -3730,8 +3730,7 @@ void CallData::ApplyServiceConfigToCallLocked(grpc_call_element* elem) {
     // from the client API, reset the deadline timer.
     if (chand->deadline_checking_enabled() && method_params_->timeout() != 0) {
       const grpc_millis per_method_deadline =
-          grpc_timespec_to_millis_round_up(
-              gpr_cycle_counter_to_time(call_start_time_)) +
+          grpc_cycle_counter_to_millis_round_up(call_start_time_) +
           method_params_->timeout();
       if (per_method_deadline < deadline_) {
         deadline_ = per_method_deadline;
diff --git a/src/core/lib/iomgr/exec_ctx.cc b/src/core/lib/iomgr/exec_ctx.cc
index a847b4dcefc..5cb778de98e 100644
--- a/src/core/lib/iomgr/exec_ctx.cc
+++ b/src/core/lib/iomgr/exec_ctx.cc
@@ -52,6 +52,7 @@ static void exec_ctx_sched(grpc_closure* closure, grpc_error* error) {
 }
 
 static gpr_timespec g_start_time;
+static gpr_cycle_counter g_start_cycle;
 
 static grpc_millis timespec_to_millis_round_down(gpr_timespec ts) {
   ts = gpr_time_sub(ts, g_start_time);
@@ -101,6 +102,16 @@ grpc_millis grpc_timespec_to_millis_round_up(gpr_timespec ts) {
       gpr_convert_clock_type(ts, g_start_time.clock_type));
 }
 
+grpc_millis grpc_cycle_counter_to_millis_round_down(gpr_cycle_counter cycles) {
+  return timespec_to_millis_round_down(
+      gpr_time_add(g_start_time, gpr_cycle_counter_sub(cycles, g_start_cycle)));
+}
+
+grpc_millis grpc_cycle_counter_to_millis_round_up(gpr_cycle_counter cycles) {
+  return timespec_to_millis_round_up(
+      gpr_time_add(g_start_time, gpr_cycle_counter_sub(cycles, g_start_cycle)));
+}
+
 static const grpc_closure_scheduler_vtable exec_ctx_scheduler_vtable = {
     exec_ctx_run, exec_ctx_sched, "exec_ctx"};
 static grpc_closure_scheduler exec_ctx_scheduler = {&exec_ctx_scheduler_vtable};
@@ -117,7 +128,13 @@ void ExecCtx::TestOnlyGlobalInit(gpr_timespec new_val) {
 }
 
 void ExecCtx::GlobalInit(void) {
+  // gpr_now(GPR_CLOCK_MONOTONIC) incurs a syscall. We don't actually know the
+  // exact cycle the time was captured, so we use the average of cycles before
+  // and after the syscall as the starting cycle.
+  const gpr_cycle_counter cycle_before = gpr_get_cycle_counter();
   g_start_time = gpr_now(GPR_CLOCK_MONOTONIC);
+  const gpr_cycle_counter cycle_after = gpr_get_cycle_counter();
+  g_start_cycle = (cycle_before + cycle_after) / 2;
   gpr_tls_init(&exec_ctx_);
 }
 
diff --git a/src/core/lib/iomgr/exec_ctx.h b/src/core/lib/iomgr/exec_ctx.h
index daf019c41ee..0ccf2a878bf 100644
--- a/src/core/lib/iomgr/exec_ctx.h
+++ b/src/core/lib/iomgr/exec_ctx.h
@@ -26,6 +26,7 @@
 #include <grpc/support/cpu.h>
 #include <grpc/support/log.h>
 
+#include "src/core/lib/gpr/time_precise.h"
 #include "src/core/lib/gpr/tls.h"
 #include "src/core/lib/gprpp/fork.h"
 #include "src/core/lib/iomgr/closure.h"
@@ -58,6 +59,8 @@ extern grpc_closure_scheduler* grpc_schedule_on_exec_ctx;
 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);
+grpc_millis grpc_cycle_counter_to_millis_round_down(gpr_cycle_counter cycles);
+grpc_millis grpc_cycle_counter_to_millis_round_up(gpr_cycle_counter cycles);
 
 namespace grpc_core {
 /** Execution context.