Threading and the Garbage handler mess.

[Sergey Gromov]

Craig Black <cblack at ara.com> wrote:
> 
> > There *should* be a
> > benefit from collecting garbage in parallel, especially after number of
> > cores raises to dozens.
> 
> Do you know something I don't?  According to my research, a separate thread 
> touching everyone else's memory causes huge amounts of cache misses and page 
> faults.  These far outweigh any benefit gleaned from running the GC in 
> parallel.

A 'separate thread touching everyone else's memory' would inevitably 
require to pause 'everyone' so that wasn't what I was talking about.  I 
was talking about a hypothetical situation when every thread were 
collecting its own garbage leaving other threads' garbage alone.  This 
approach, assuming large amounts of thread-local garbage, would 
definitely benefit from parallelization.  But, even being hypothetical, 
it couldn't be free, and inevitable overhead may outweight benefits if 
number of parallel units is small.