Re: Struct is slow

2007/10/17, Joel VanderWerf <vjoel@xxxxxxxxxxxxxxxxx>:
Sylvain Joyeux wrote:
I'm not sure whether you are familiar with Benchmark#bmbm which does a
rehearsal - personally I rather not switch off GC since in realistic
situations GC time belongs into the mix. But results are rather
similar:
Sure. GC does belong to the mix. Now, if GC is enabled you are not able to
compare anything. Let's assume that GC runs during 'array init', you will
say 'hey, struct init is faster'. Now, if GC runs during 'struct init' the
result may change ...

But you have a *lot* invocations and it's highly unlikely that GC runs
during every init. On the other hand, if you allocate a lot of memory
from OS that may slow things down. And this will happen without GC.

Also, IMHO cost of memory GC overhead is also part of the runtime
performance. If you compare two approaches and one allocates a lot
more memory than the other, then GC times belong in the measurement
because in a real application that approach will also lead to
increased GC overhead.

Keeping GC is meaningful when benchmarking a whole application. In
microbenchmarks like these, it is simply noise.

For fairness, you could do it this way (assuming REP is large enough):

...
Benchmark.bmbm 15 do |x|
GC.start
x.report 'struct init' do
REP.times { Foo.new data, data }
GC.start
end

GC.start
x.report 'array init' do
REP.times { [data, data] }
GC.start
end
...

GC.start is not guaranteed to actually run GC AFAIK. I'd probably rather do

Benchmark.bmbm do
GC.stop
# tests
GC.start
end

There is a chance that GC.start will clean up all the memory allocated
during the first run.

Kind regards

robert

.

Relevant Pages

  • Re: Struct is slow
    ... situations GC time belongs into the mix. ... if GC runs during 'struct init' the ... IMHO cost of memory GC overhead is also part of the runtime ...
    (comp.lang.ruby)
  • Re: Struct is slow
    ... rehearsal - personally I rather not switch off GC since in realistic ... situations GC time belongs into the mix. ... if GC runs during 'struct init' the ... microbenchmarks like these, it is simply noise. ...
    (comp.lang.ruby)