don't call xpti if there are no subscribers

This avoids the overhead of preparing data for xpti,
and the cost of the xpti call itself, if nothing is
subscribed to the ur.call xpti call stream.

Author: pbalcer

CMakeLists.txt

@@ -137,7 +137,7 @@ if(UR_ENABLE_TRACING)
 
     if (UR_BUILD_XPTI_LIBS)
         # fetch xpti proxy library for the tracing layer
-        FetchContentSparse_Declare(xpti https://github.com/intel/llvm.git "sycl-nightly/20230703" "xpti")
+        FetchContentSparse_Declare(xpti https://github.com/intel/llvm.git "nightly-2024-10-22" "xpti")
         FetchContent_MakeAvailable(xpti)
 
         # set -fPIC for xpti since we are linking it with a shared library
@@ -149,7 +149,7 @@ if(UR_ENABLE_TRACING)
         set(XPTI_DIR ${xpti_SOURCE_DIR})
         set(XPTI_ENABLE_TESTS OFF CACHE INTERNAL "Turn off xptifw tests")
 
-        FetchContentSparse_Declare(xptifw https://github.com/intel/llvm.git "sycl-nightly/20230703" "xptifw")
+        FetchContentSparse_Declare(xptifw https://github.com/intel/llvm.git "nightly-2024-10-22" "xptifw")
 
         FetchContent_MakeAvailable(xptifw)
 

examples/collector/collector.cpp

@@ -125,8 +125,7 @@ XPTI_CALLBACK_API void xptiTraceInit(unsigned int major_version,
         return;
     }
     if (std::string_view(stream_name) != UR_STREAM_NAME) {
-        std::cout << "Invalid stream name: " << stream_name << ". Expected "
-                  << UR_STREAM_NAME << ". Aborting." << std::endl;
+        // we expect ur.call, but this can also be xpti.framework.
         return;
     }
 

source/loader/layers/tracing/ur_tracing_layer.cpp

@@ -15,6 +15,7 @@
 #include "xpti/xpti_data_types.h"
 #include "xpti/xpti_trace_framework.h"
 #include <atomic>
+#include <cstdint>
 #include <optional>
 #include <sstream>
 
@@ -59,6 +60,12 @@ void context_t::notify(uint16_t trace_type, uint32_t id, const char *name,
 }
 
 uint64_t context_t::notify_begin(uint32_t id, const char *name, void *args) {
+    // we use UINT64_MAX as a special value that means "tracing disabled",
+    // so that we don't have to repeat this check in notify_end.
+    if (!xptiCheckTraceEnabled(call_stream_id)) {
+        return UINT64_MAX;
+    }
+
     if (auto loc = codelocData.get_codeloc()) {
         xpti::payload_t payload =
             xpti::payload_t(loc->functionName, loc->sourceFile, loc->lineNumber,
@@ -77,6 +84,10 @@ uint64_t context_t::notify_begin(uint32_t id, const char *name, void *args) {
 
 void context_t::notify_end(uint32_t id, const char *name, void *args,
                            ur_result_t *resultp, uint64_t instance) {
+    if (instance == UINT64_MAX) { // tracing disabled
+        return;
+    }
+
     notify((uint16_t)xpti::trace_point_type_t::function_with_args_end, id, name,
            args, resultp, instance);
 }

test/layers/tracing/test_collector.cpp

@@ -49,8 +49,7 @@ XPTI_CALLBACK_API void xptiTraceInit(unsigned int major_version,
         return;
     }
     if (std::string_view(stream_name) != UR_STREAM_NAME) {
-        std::cout << "Invalid stream name: " << stream_name << ". Expected "
-                  << UR_STREAM_NAME << ". Aborting." << std::endl;
+        // we expect ur.call, but this can also be xpti.framework.
         return;
     }