Re: garbage collection slowdown

["Ludovic Courtès" <ludo@gnu.org>]

Hi Han-Wen,

Great to see you back here!

Han-Wen Nienhuys <hanwenn@gmail.com> skribis:

> On Tue, Jan 28, 2020 at 11:41 PM Han-Wen Nienhuys <hanwenn@gmail.com> wrote:
>> Unfortunately, it looks like the adoption of the BDW GC library caused
>> a ~6x slowdown, causing an overall end-to-end slowdown of 50%.
>>
>> I was wondering if you folks would have tips to further tune GC for
>> wall-time speed, and if there additional diagnostics to see if we're
>> doing something extraordinarily silly.
>
> For the record, I managed to solve this, by scaling up the heap more
> aggressively. See
> https://codereview.appspot.com/561390043/diff/557260051/lily/score-engraver.cc

Weird.  It would be interesting to see where the slowdown comes from.
Overall, my recollection of the 1.8 to 2.0 transition (where we
introduced libgc) is that GC was a bit faster, definitely not slower.

That said, does LilyPond happen to use lots of bignums and/or lots of
finalizers?  Finalizers, including those on bignums, end up being very
GC-intensive, as discussed in my recent message.  Perhaps that’s what’s
happening here, for instance if you create lots of SMOBs with a free
function.

Thanks,
Ludo’.