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Diffstat (limited to 'docs/devel')
| -rw-r--r-- | docs/devel/tcg.rst | 23 |
1 files changed, 23 insertions, 0 deletions
diff --git a/docs/devel/tcg.rst b/docs/devel/tcg.rst index 136a7a0..b4096a1 100644 --- a/docs/devel/tcg.rst +++ b/docs/devel/tcg.rst @@ -188,3 +188,26 @@ memory areas instead calls out to C code for device emulation. Finally, the MMU helps tracking dirty pages and pages pointed to by translation blocks. +Profiling JITted code +--------------------- + +The Linux ``perf`` tool will treat all JITted code as a single block as +unlike the main code it can't use debug information to link individual +program counter samples with larger functions. To overcome this +limitation you can use the ``-perfmap`` or the ``-jitdump`` option to generate +map files. ``-perfmap`` is lightweight and produces only guest-host mappings. +``-jitdump`` additionally saves JITed code and guest debug information (if +available); its output needs to be integrated with the ``perf.data`` file +before the final report can be viewed. + +.. code:: + + perf record $QEMU -perfmap $REMAINING_ARGS + perf report + + perf record -k 1 $QEMU -jitdump $REMAINING_ARGS + DEBUGINFOD_URLS= perf inject -j -i perf.data -o perf.data.jitted + perf report -i perf.data.jitted + +Note that qemu-system generates mappings only for ``-kernel`` files in ELF +format. |