Changes between Version 2 and Version 3 of Debugging/LowLevelProfiling/oprofile

Timestamp:

11/03/09 08:01:00 (4 years ago)

Author:

guest

Comment:

--

Debugging/LowLevelProfiling/oprofile

@@ -19 +19 @@
 $ sudo opreport
 }}}
-check that the program you ran is at the top of the profile somewhere.  Sometimes for me it doesn't appear, and have to run it again.  To see a list of possible `<event>`s, use
-{{{
-$ opcontrol --list-events
-}}}
+check that the program you ran is at the top of the profile somewhere.  Sometimes for me it doesn't appear, and have to run it again.  To see a list of possible `<event>`s, use `$ opcontrol --list-events`.
 
 Then to annotate the source:
 {{{
-$ sudo opannotate --source <program> >&! log}}}
+$ sudo opannotate --source <program> >&! log
+}}}
 lists the contents of source files in order of importance.  Alternatively use --output-dir to put the source files in a directory, but then 
 you don't get to find out which are the important ones.
+
+
+== Things to be aware of ==
+
+  * You might think that you could use the `-fvia-C -optc-g` options to force GHC to export C-source-level debugging symbols.  The Evil Mangler script that post-processes the `.s` file output by `gcc` does not understand the debug annotations added by `gcc`'s `-g` flag, and so `-optc-g` will not work.  You can, however, get GHC to output assembly-level debugging symbols by using `-opta-g`.  You'll probably also want to use the `-keep-s-files` option so that `opannotate` can get at the relevant `.s` files.
+
+  * Suppose that you do 
+    {{{
+$ sudo opcontrol --setup --event=<eventname>:<count>
+    }}}
+    and receive an error message that "Count `<count>` for event `<eventname>` is below the minimum."  If you check the minimum value for
+    `<eventname>` using the `--list-events` option and see that `<count>` is in fact not below the purported minimum count, then you may have passed
+    in a non-zero value for `--callgraph` option.  When doing callgraph profiling, OProfile requires that the sample count be at least 15 times the
+    minimum.
+    [[BR]][[BR]]
+    `opcontrol --status` will show you if callgraph is currently set.  To reset it, make sure the oprofile daemon is stopped and reset the callgraph
+    value:
+    {{{
+$ sudo opcontrol --shutdown
+$ sudo opcontrol --callgraph=0
+    }}}
+    Now you can re-run your profiling and the original `<count>` should work.
+