Re: Garbage collector tuning?

[Jan Wedekind]

On Thu, 10 Sep 2015, Ludovic Courtès wrote:
> Jan Wedekind <address@hidden> skribis:
>
> > I wonder whether there is a more performant way to allocate larger
> > memory blocks (e.g. 1 MByte). "gc-malloc-pointerless" seems to be much
> > slower than "malloc":
> >
> >                                            user     system      total        
> > real
> >     Guile allocate memory              0.003780   0.000020   0.003800 (  
> > 0.003810)
> >     C allocate memory                  0.000060   0.000000   0.000060 (  
> > 0.000070)
>
> It isn’t fair to compare GC_malloc_pointerless with malloc.  Instead, it
> should be compared with interleaved malloc + free sequences.
>
> You should find more on this topic on the home page of libgc, the GC
> that Guile uses: <http://www.hboehm.info/gc/>

Yes, I agree. The sequence malloc, free, malloc, free, ... is not a 
representative use-pattern. However I only forced a single garbage 
collector run for a 1000 tests.
The full benchmark is here by the way:

                                           user     system      total        
real
    Guile GOOPS method dispatch        0.000060   0.000000   0.000060 (  
0.000050)
    Guile make empty sequence          0.000690   0.000000   0.000690 (  
0.000700)
    Guile allocate memory              0.003760   0.000020   0.003780 (  
0.003800)
    Guile negate empty sequence        0.003500   0.000080   0.003580 (  
0.003580)
    Guile make sequence                0.002620   0.000020   0.002640 (  
0.002660)
    Guile negate sequence              0.006980   0.000030   0.007010 (  
0.007030)
    C allocate memory                  0.000060   0.000000   0.000060 (  
0.000070)
    C negate empty sequence            0.000050   0.000000   0.000050 (  
0.000040)
    C negate sequence                  0.000720   0.000000   0.000720 (  
0.000720)


> > Is there a way to control how often the garbage collector is run?
>
> The file doc/README.environment in libgc describes some useful
> environment variables, notably these:
>
>  GC_INITIAL_HEAP_SIZE=<bytes> -   Initial heap size in bytes.  May speed up
>                                  process start-up.
>
>  GC_MAXIMUM_HEAP_SIZE=<bytes> - Maximum collected heap size.
>
>  GC_MARKERS=<n> - Linux w/threads and parallel marker only.  Set the number
>                  of marker threads.  This is normally set to the number of
>                  processors.  It is safer to adjust GC_MARKERS than GC_NPROCS,
>                  since GC_MARKERS has no impact on the lock implementation.
>
> Guile also honors the ‘GC_FREE_SPACE_DIVISOR’ environment variable.  See
> the comments in gc.h for the meaning of this one.

Ok, I'll play around with it. Thanks for the information.

> HTH,
> Ludo’.