JIT status: how to introspect

[Michael Truog]

On 2/27/21 8:52 AM, Max Lapshin wrote:
> I've read this article:
> https://www.erlang-solutions.com/blog/performance-testing-the-jit-compiler-for-the-beam-vm/
>
> and I see that perf top shows functions that are looking like  $gen_server2_loop
>
> When I launch my flussonic with erl 24, I do not see any functions
> with this pattern, only functions from C.
>
> So this is why I want to understand: is JIT working or I haven't
> launched it at all?
If erlang:system_info(emu_flavor) returns jit it should be working.  You 
should be able to see a difference if you profile the execution with and 
without to determine how the jit execution changes performance.

Best Regards,
Michael


> On Wed, Feb 24, 2021 at 10:43 PM Max Lapshin <max.lapshin@REDACTED> wrote:
>> 23.77% beam.smp [.] ac_find_all_non_overlapping
>> 13.11% libc-2.27.so [.] __memmove_avx_unaligned_erms
>>
>> I think that it is rather clear that we need to do something with
>> binary:split(..., [global])
>>
>> On Wed, Feb 24, 2021 at 8:57 PM Dan Gudmundsson <dgud@REDACTED> wrote:
>>> All code is jit-compiled, so there is nothing to check.
>>>
>>> The jit helps sequentiell code only, if that is not your bottleneck you will not see any speedup.
>>> as if your current code uses a lot of bif's/nif's and message passing.
>>> And I guess there is still minor stuff that can be improved.
>>>
>>> On Wed, Feb 24, 2021 at 6:01 PM Max Lapshin <max.lapshin@REDACTED> wrote:
>>>> Hi.
>>>>
>>>> I've tried to launch our flussonic under jit.
>>>>
>>>> Thank you a lot for this work.  We got zero speedup, but perf top have
>>>> showed where we can achieve up to 20% of boost (or maybe more).
>>>>
>>>>
>>>> Is it possible to introspect current jit status?  Something like:
>>>>
>>>>
>>>>> jit:info().
>>>> #{
>>>>    calls => ...
>>>>     misses => ...
>>>>     ...
>>>> }
>>>>
>>>> or what do you use to check it in runtime?

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