Re: [Sablevm-developer] Threading support in SableVM

[Chris P. <chr...@ma...>]

Grzegorz B. Prokopski wrote:

> Chris, have you looked at these regressions again? Are they present
> in current staging version too? 

Yes (I just checked).  But I am not sure if it's a regression.  I was 
seeing weird multithreading behaviour with mtrt and my spmt stuff with 
my changes against 1.0.8 -- and while I do not know for sure, my 
intuition at the time (after looking at many instruction traces) was 
that the spmt was slowing down threads long enough for concurrency 
issues with ordinary threads to appear.

Do you have some traces about what
> exactly is happenning? Could you maybe try to debug sablevm behavior?

I posted a while ago asking for more help about this (see message with 
gdb log in response to David)

It fails in _svmf_enter_object_monitor().  I think Etienne needs to look 
at it because he wrote the locking stuff ... I would like to participate 
in debugging it but I don't know where to begin.  Should we try, for 
example, removing thin locks altogether and see if that fixes it?  Or 
try making some critical sections bigger?

> I think that from active developers you might be the person most
> interested in multithreading (and simultanous execution in general),
> so this naturally makes you our 'Multithreading Expert'.

Well, I would say Etienne and Clark are the multithreading experts. 
David likely knows more than me too ... I haven't actually started 
touching pthreads yet in my code.

> This way or another we need to track this issue and fix this. Not being
> able to run benchmarks is *bad* thing in research (and this has impact
> on practical usefulness too!). Looking at it in the long term - do you
> think it would be feasible to create our own test cases/min-apps that
> would stretch and excersise SableVM's threads? 

The JGF benchmarks include many micro benchmarks.  They really are a lot 
more useful than SPEC and JOlden, in my opinion, for finding 
small-yet-critical bugs and optimizing performance of specific things.

> But of course the first thing now would be to track this issue and try
> to fix it. I guess David could help w/ Classpath/SableVM glue code as he
> has lots of experience there and this is most probably the source of
> our problems.


Can somebody check this quickly on 1.0.9 or an earlier version?

Maybe all of the Montreal developers should get together to discuss 
1.1.0, and plans for the future?  We haven't had a multiple person 
meeting (at least one that involved me!) in a long time ...

Cheers,
Chris