[gambit-list] parallel GC

Adam adam.mlmb at gmail.com
Mon Nov 7 21:50:53 EST 2016


Aha. Just out of general interest,

 * Per GC cycle, how much time are we talking on a random 2Ghz machine, and
presuming all GVM threads run all-safe-declared Scheme code only?


 * What is the mechanism of the sync to initiate a GC iteration - the first
initiating thread setting some global variable, msyinc:ing, and all other
GVM threads polling it all the time, or/and by sending some kind of
interrupt signal via OS facilities?

 * What is the mechanism of the sync for different GC stages - ...?


2016-11-08 10:19 GMT+08:00 Marc Feeley <feeley at iro.umontreal.ca>:

> The fact is that there is some synchronization overhead when the GC is
> parallel (the OS threads need to synchronize to run the GC and each of the
> phases of the GC in unison).  So if the heap is small, as is the case for
> most unit tests, the GC doesn’t accelerate much because there is little
> parallelism to exploit, but there is an overhead to pay for attempting to
> do things in parallel.  This is a common issue in parallel processing.
>
> Marc
>
> > On Nov 7, 2016, at 8:53 PM, Adam <adam.mlmb at gmail.com> wrote:
> >
> > And this shows us what?
> >
> > Btw, isn't the only effect --enable-multiple-threaded-vms should have
> right now, that execution is slightly faster, as GC is faster now?
> >
> > 2016-11-08 9:31 GMT+08:00 Bradley Lucier <lucier at math.purdue.edu>:
> > On 11/07/2016 08:26 PM, Adam wrote:
> > Wait, what does this actually tell us?
> >
> > There used to be a big difference in the time to complete the unit
> tests: with  --enable-multiple-threaded-vms it used to take
> >
> > [ 122|   0|   0] 100% ##########################################   3.7s
> >
> > and now it takes
> >
> > [ 122|   0|   0] 100% ##########################################   1.8s
> >
> > A big improvement.  But without --enable-multiple-threaded-vms it takes
> >
> > [ 122|   0|   0] 100% ##########################################   1.6s
> >
> > So there's been an improvement.
> >
> > Brad
> >
> > _______________________________________________
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>
>
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