LNT: Fix Perf profiling support

[tnfchris]

Summary

In Python3 the C interface has changed. [1]

During the upgrade the Creation of the perf
interface was upgraded to Python3 but the initialization
itself was not. As a consequence the module was not actually
registered and trying to use perf results in an error.

This would not be noticed as the import in the Python module
has the import in a try: .. except: pass block presumably
because perf support is optional.

[1] http://python3porting.com/cextensions.html

[thopre]

lnt/testing/profile/perf.py

15

Why did Python2 not require this? Is there some sort of module path set somewhere that does not work for Python3?

[tnfchris]

lnt/testing/profile/perf.py

15

from what I understood, C Python code will be created in the same folder as it's defined in and those folder become the module path.
I don't know the semantics of Python 2 as I didn't look at it, but 3 would require the full path or module path set somewhere.

I had looked through the configuration and this was not set anywhere so I opted for using the full import.

[thopre]

lnt/testing/profile/perf.py

15

Oh I think it's because Python2 defaults to relative import before full import. I would therefore suggest to use instead:

from . import cPerf

[tnfchris]

lnt/testing/profile/perf.py

15

fancy.. didn't know that, thanks.

[thopre]

lnt/testing/profile/perf.py

15

FYI: https://docs.python.org/3/reference/import.html#package-relative-imports

There's a PEP somewhere with more details, couldn't find the link in less than 10s so I got lazy.

[tnfchris]

use package relative import syntax

[thopre]

lnt/testing/profile/perf.py

10–17

Sorry I forgot to mention that the relative import syntax is available in Python 2.7. So you can just change the import cPerf into from . import cPerf and nothing else (i.e. 1 line change)

[thopre]

LGTM

lnt/testing/profile/cPerf.cpp

                                      nullptr};
 #endif
 
-PyMODINIT_FUNC initcPerf(void) {
 #if PY_MAJOR_VERSION >= 3
+PyMODINIT_FUNC PyInit_cPerf(void) {
   return PyModule_Create(&cPerfModuleDef);
+}
 #else
+PyMODINIT_FUNC initcPerf(void) {
   (void)Py_InitModule("cPerf", cPerfMethods);
-#endif
 }
+#endif
 
 #else // STANDALONE
 

lnt/testing/profile/perf.py

 import traceback
 
 try:
-    import cPerf
+    from . import cPerf
 except Exception:
     pass