Re: Perf support for interpreted and Just-In-Time translated olanguages

[Andi Kleen <andi@firstfloor.org>]

> I understood that there is a way to ask for the current JITted code ->
> symtab, my question was specifically about how to get notifications when
> those mappings change.

JVMTI has a callback interface, so you can register call backs for
specific events:

http://docs.oracle.com/javase/7/docs/platform/jvmti/jvmti.html#EventSection

> When we use mmap(addr, len, PROT_EXEC) the kernel has a meta event
> called PERF_RECORD_MMAP that will record addr range, symtab DSO path,
> and we ask it to be timestamped, how to do that for the equivalent part
> in the JVM?

The CompiledMethodLoad callback would trigger that event.

> 
> My initial thought was to find that using perf probe and insert there a
> probe point, but I think that there may be already an existing
> tracepoint in the jvm for that, one that, from what I've read so far,
> is _not_ being used by this java perf agent, right?

It's not needed. Java already has all the needed hooks.

Maybe for some different JITs.

> 
> From what I understood, how would it insert that event into the
> perf.data event stream? Only if it necessarily involved a new mmap, via
> the kernel, etc.

That's the new interface to be defined.

Just write a perf.data?

-Andi


-- 
ak@linux.intel.com -- Speaking for myself only.