Pass call start time into the call stack via grpc_call_element_args.

src/core/ext/census/grpc_filter.c

@@ -133,7 +133,7 @@ static grpc_error *client_init_call_elem(grpc_exec_ctx *exec_ctx,
   call_data *d = elem->call_data;
   GPR_ASSERT(d != NULL);
   memset(d, 0, sizeof(*d));
-  d->start_ts = gpr_now(GPR_CLOCK_REALTIME);
+  d->start_ts = args->start_time;
   return GRPC_ERROR_NONE;
 }
 
@@ -152,7 +152,7 @@ static grpc_error *server_init_call_elem(grpc_exec_ctx *exec_ctx,
   call_data *d = elem->call_data;
   GPR_ASSERT(d != NULL);
   memset(d, 0, sizeof(*d));
-  d->start_ts = gpr_now(GPR_CLOCK_REALTIME);
+  d->start_ts = args->start_time;
   /* TODO(hongyu): call census_tracing_start_op here. */
   grpc_closure_init(&d->finish_recv, server_on_done_recv, elem);
   return GRPC_ERROR_NONE;

src/core/ext/client_config/client_channel.c

@@ -881,9 +881,7 @@ static grpc_error *cc_init_call_elem(grpc_exec_ctx *exec_ctx,
   // Initialize data members.
   grpc_deadline_state_init(exec_ctx, elem, args->call_stack);
   calld->path = GRPC_MDSTR_REF(args->path);
-  // TODO(roth): Is there a better value to use here for the actual start
-  // time of the call (i.e., something initialized at the surface layer)?
-  calld->call_start_time = gpr_now(GPR_CLOCK_MONOTONIC);
+  calld->call_start_time = args->start_time;
   calld->deadline = gpr_convert_clock_type(args->deadline, GPR_CLOCK_MONOTONIC);
   calld->wait_for_ready_from_service_config = WAIT_FOR_READY_UNSET;
   calld->cancel_error = GRPC_ERROR_NONE;

src/core/lib/channel/channel_stack.c

@@ -179,6 +179,7 @@ grpc_error *grpc_call_stack_init(
 
   /* init per-filter data */
   grpc_error *first_error = GRPC_ERROR_NONE;
+  args.start_time = gpr_now(GPR_CLOCK_MONOTONIC);
   for (i = 0; i < count; i++) {
     args.call_stack = call_stack;
     args.server_transport_data = transport_server_data;

src/core/lib/channel/channel_stack.h

@@ -75,6 +75,7 @@ typedef struct {
   const void *server_transport_data;
   grpc_call_context_element *context;
   grpc_mdstr *path;
+  gpr_timespec start_time;
   gpr_timespec deadline;
 } grpc_call_element_args;