Enabling PerfJITEventListener in the XLA runtime

[Muneeb Anwar]

Hi,

I am trying to use perf tools (record/report) to profile JITed functions, when using OrcJIT in the XLA runtime. Even though there's this option to register `PerfJITEventListener` by setting `enable_perf_listener`, the call to `llvm::JITEventListener::createPerfJITEventListener()` returns NULL showing that it failed.

Moreover, the online documentation for OrcJIT in the llvm-project says that `JITEventListeners` feature isn't supported. This confuses me as to why there is an option for this if it's not supported in llvm.

How is OrcJIT supposed to make use of `PerfJITEventListener`? And how can it be enabled in the XLA runtime (if possible at all)? 

If not, is there another way to profile JITed code?

best,

Muneeb

[Eugene Zhulenev]

Hi Muneeb,

It should work:

1. perf record -k 1 -g -o /tmp/perf.data -- $run_openxla_command (i.e. it can be jax)

2. perf inject -j -i /tmp/perf.data -o /tmp/perf.data.jit

3. perf report -g -i /tmp/perf.data

It requires defining LLVM_USE_PERF (we define it in lvm/include/llvm/Config/llvm-config.h), I'm not super familiar with OSS build set up, but I guess you can always pass if via bazel --copt flag.

Also I suspect we might be building jaxlib without this flag (+Peter to confirm or deny).

Eugene

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[Peter Hawkins]

Hmm.. indeed we're not building jaxlib with that flag.

Is there a cost to doing so, or should we enable it unconditionally?

Peter

[Eugene Zhulenev]

On Fri, Sep 6, 2024 at 12:54 PM Peter Hawkins <phaw...@google.com> wrote:

Hmm.. indeed we're not building jaxlib with that flag.

Is there a cost to doing so, or should we enable it unconditionally?

~free, it dumps extra metadata for perf to /tmp, and sometimes logs warnings if /tmp is not writable. It's super useful for debugging, I vote for enabling it by default for jaxlib.

Eugene