Re: Some benchmarks

["Iñaki Baz Castillo" <ibc@aliax.net>]

2010/12/22 Eric Wong <normalperson@yhbt.net>:
>> I don't understand why in the last test (big file, 1000 copies)
>> io_splice takes so long, maybe it takes more time initializing each
>> object within the benchmark block?
>
> It'ls likely the test wrote enough to force blocking writes to disk,
> and your disk is now the bottleneck.  In that case, all the memory
> tricks in the world won't help :)

Aha, it makes sense.


> Try it on a tmpfs mount.

Yes, that would be my next test.


> Also, relying on GC to close file descriptors could be a small
> performance problem given the number of iterations.

Well, this is just a strange use case test. Indeed I should call
File.close by myself.



>>    # We use a pipe as a ring buffer in kernel space.
>>    # pipes may store up to IO::Splice::PIPE_CAPA bytes
>>    pipe = IO.pipe
>
> You can reuse the pipe object through multiple runs assuming you drain
> it properly.

So I need to learn what "draining a pipe" means. I assume I need to
empty/rewind it. I suppose there ar API methods for this.



>> I've tryed to declare source, source_fd and pipe = IO.pipe before the
>> benchmark block but then I get empty copied files (I need to declare
>> all of them within the benchmark block). I assume the test script can
>> be improved.
>
> You need to rewind source if you don't specify an input offset for splice.
> Likewise for the dest and destination offset.  The open+close is part of
> the test for the FileUtils things, though, so I would just open close
> (you were leaving the close up to GC, which usually fine for MRI but not
> for benchmark purposes).

Ok. Thanks a lot!



-- 
Iñaki Baz Castillo
<ibc@aliax.net>