Forcing apps to collect GC stats?

[Edward Kmett]

Interesting.

I suppose ekg could also (ab)use this.

Johan?

-Edward


On Thu, Jul 31, 2014 at 5:51 AM, Simon Marlow <marlowsd at gmail.com> wrote:

> Hey Bryan,
>
> Sorry for the delay.
>
>
> On 15/07/14 01:57, Bryan O'Sullivan wrote:
>
>> I spent a bit of time over the weekend trying to figure out how to force
>> the RTS to collect GC statistics, but was unable to do so.
>>
>> I'm currently working on enriching criterion's ability to gather data,
>> among which I'd like to see GC statistics. If I try to obtain GC stats
>> using criterion when I'm not running the benchmark app with +RTS -T, I
>> get an exception.
>>
>> Is there a way to allow criterion to forcibly enable stats collection?
>> My efforts to do so have gotten me nowhere. It would be unfortunate if I
>> had to tell users of criterion that they should always run with +RTS -T
>> or add a -rtsopts clause, as they'll simply forget.
>>
>> And while I'm asking, why does GHC not simply collect GC stats by
>> default? Collecting them seems to have zero cost, from what I can see?
>>
>
> So you can do this in the same way as GHC. See
>
> https://phabricator.haskell.org/diffusion/GHC/browse/
> master/ghc/hschooks.c;6fa6caad0cb4ba99b2c0b444b0583190e743dd63$18-28
>
> Which is imported into Haskell like this:
>
> https://phabricator.haskell.org/diffusion/GHC/browse/master/ghc/Main.hs;
> 6fa6caad0cb4ba99b2c0b444b0583190e743dd63$847-848
>
> I'm not sure why it's marked "safe", but it doesn't hurt.
>
> This API is kind-of public, in the sense that we deliberately expose it
> via the Rts.h header, and I'll try not to break it gratuitously.
>
> Cheers,
> Simon
>
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