Core; fix avoidable work (allocs+CPU) when logs enabled but trace level means work will not be used (#31098)

core; ref #30979

1. avoid calling `grpc_dump_slice` if the log level is too low (and the
result will be ignored)
2. use `GRPC_TRACE_FLAG_ENABLED(x)` over `x.enabled()` in the touched
code

---------

Co-authored-by: Yash Tibrewal <yashkt@google.com>

src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc

@@ -1162,13 +1162,15 @@ void GrpcLb::BalancerCallState::OnBalancerMessageReceivedLocked() {
   upb::Arena arena;
   if (!GrpcLbResponseParse(response_slice, arena.ptr(), &response) ||
       (response.type == response.INITIAL && seen_initial_response_)) {
-    char* response_slice_str =
-        grpc_dump_slice(response_slice, GPR_DUMP_ASCII | GPR_DUMP_HEX);
-    gpr_log(GPR_ERROR,
-            "[grpclb %p] lb_calld=%p: Invalid LB response received: '%s'. "
-            "Ignoring.",
-            grpclb_policy(), this, response_slice_str);
-    gpr_free(response_slice_str);
+    if (gpr_should_log(GPR_LOG_SEVERITY_ERROR)) {
+      char* response_slice_str =
+          grpc_dump_slice(response_slice, GPR_DUMP_ASCII | GPR_DUMP_HEX);
+      gpr_log(GPR_ERROR,
+              "[grpclb %p] lb_calld=%p: Invalid LB response received: '%s'. "
+              "Ignoring.",
+              grpclb_policy(), this, response_slice_str);
+      gpr_free(response_slice_str);
+    }
   } else {
     switch (response.type) {
       case response.INITIAL: {

src/core/lib/iomgr/endpoint_cfstream.cc

@@ -113,7 +113,8 @@ static grpc_error_handle CFStreamAnnotateError(grpc_error_handle src_error,
 }
 
 static void CallReadCb(CFStreamEndpoint* ep, grpc_error_handle error) {
-  if (grpc_tcp_trace.enabled()) {
+  if (GRPC_TRACE_FLAG_ENABLED(grpc_tcp_trace) &&
+      gpr_should_log(GPR_LOG_SEVERITY_DEBUG)) {
     gpr_log(GPR_DEBUG, "CFStream endpoint:%p call_read_cb %p %p:%p", ep,
             ep->read_cb, ep->read_cb->cb, ep->read_cb->cb_arg);
     size_t i;
@@ -225,7 +226,8 @@ static void WriteAction(void* arg, grpc_error_handle error) {
       EP_UNREF(ep, "write");
     }
 
-    if (grpc_tcp_trace.enabled()) {
+    if (GRPC_TRACE_FLAG_ENABLED(grpc_tcp_trace) &&
+        gpr_should_log(GPR_LOG_SEVERITY_DEBUG)) {
       grpc_slice trace_slice = grpc_slice_sub(slice, 0, write_size);
       char* dump = grpc_dump_slice(trace_slice, GPR_DUMP_HEX | GPR_DUMP_ASCII);
       gpr_log(GPR_DEBUG, "WRITE %p (peer=%s): %s", ep, ep->peer_string.c_str(),

src/core/lib/iomgr/tcp_windows.cc

@@ -203,7 +203,8 @@ static void on_read(void* tcpp, grpc_error_handle error) {
         }
         GPR_ASSERT((size_t)info->bytes_transferred == tcp->read_slices->length);
 
-        if (grpc_tcp_trace.enabled()) {
+        if (GRPC_TRACE_FLAG_ENABLED(grpc_tcp_trace) &&
+            gpr_should_log(GPR_LOG_SEVERITY_INFO)) {
           size_t i;
           for (i = 0; i < tcp->read_slices->count; i++) {
             char* dump = grpc_dump_slice(tcp->read_slices->slices[i],
@@ -353,7 +354,8 @@ static void win_write(grpc_endpoint* ep, grpc_slice_buffer* slices,
   WSABUF* buffers = local_buffers;
   size_t len, async_buffers_offset = 0;
 
-  if (grpc_tcp_trace.enabled()) {
+  if (GRPC_TRACE_FLAG_ENABLED(grpc_tcp_trace) &&
+      gpr_should_log(GPR_LOG_SEVERITY_INFO)) {
     size_t i;
     for (i = 0; i < slices->count; i++) {
       char* data =

src/core/lib/security/transport/secure_endpoint.cc

@@ -236,7 +236,8 @@ static void flush_read_staging_buffer(secure_endpoint* ep, uint8_t** cur,
 }
 
 static void call_read_cb(secure_endpoint* ep, grpc_error_handle error) {
-  if (GRPC_TRACE_FLAG_ENABLED(grpc_trace_secure_endpoint)) {
+  if (GRPC_TRACE_FLAG_ENABLED(grpc_trace_secure_endpoint) &&
+      gpr_should_log(GPR_LOG_SEVERITY_INFO)) {
     size_t i;
     for (i = 0; i < ep->read_buffer->count; i++) {
       char* data = grpc_dump_slice(ep->read_buffer->slices[i],
@@ -394,7 +395,8 @@ static void endpoint_write(grpc_endpoint* secure_ep, grpc_slice_buffer* slices,
 
     grpc_slice_buffer_reset_and_unref(&ep->output_buffer);
 
-    if (GRPC_TRACE_FLAG_ENABLED(grpc_trace_secure_endpoint)) {
+    if (GRPC_TRACE_FLAG_ENABLED(grpc_trace_secure_endpoint) &&
+        gpr_should_log(GPR_LOG_SEVERITY_INFO)) {
       for (i = 0; i < slices->count; i++) {
         char* data =
             grpc_dump_slice(slices->slices[i], GPR_DUMP_HEX | GPR_DUMP_ASCII);