ForeignPtr reloaded

[Donald Bruce Stewart]

bulat.ziganshin:
> Hello Donald,
> 
> Sunday, June 4, 2006, 11:22:24 AM, you wrote:
> 
> > I got around to writing a benchmark for testing out tuned foreign
> > pointer implementations with byte strings. In tests allocating between
> > 1M and 100M foreign pointers, I found around a 5% speed up and 5% less
> > space usage, using the tuned finalizer-less ForeignPtr described in the
> > attached patch, over the current design -- as Bulat has always suggested
> > I would find :)
> 
> > The effect wasn't as easy to observe with fewer numbers. However, I now
> 
> hmmm.. for each ForeignPtr you should see about 10 bytes profit, so
> for 1m-100m ptrs total gain should be 10mb-1gb. how much percents -
> depends entirely on the size of each string.
> 
> speed improvement depends on operations tested. afaik, this
> change should make creation of ByteStrings faster, so i hope that it
> will make faster reading of ByteStrings what is now 1.5-2 times
> slower than writing in my Streams library (with ghc 6.4):
> 
> vPutChar: 0.891 secs (user: 0.851 secs)
> vGetChar: 0.771 secs (user: 0.771 secs)
> 
> vPutBuf20: 0.491 secs (user: 0.391 secs)
> vGetBuf20: 0.461 secs (user: 0.461 secs)
> 
> vPutByteStrLn20: 0.992 secs (user: 0.991 secs)         --- see the difference
> vGetByteLine20 : 1.793 secs (user: 1.622 secs)         --- between these 2 lines
> vGetByteLineContents20: 2.343 secs (user: 2.243 secs)
> 
> vPutStrLn20: 2.494 secs (user: 2.323 secs)
> vGetLine20 : 7.701 secs (user: 7.130 secs)
> vGetContents: 13.710 secs (user: 12.798 secs)
> 
> 
> > have a good use case where we will care about this: lazy bytestrings.
> > They used chunked lists of bytestrings to handle large amounts of input.
> > Each chunk needs its own foreign pointer. This patch should thus improve
> > their performance, by avoiding the redundant ioref for the finalizer.
> 
> afaik, your lazy bytestrings is anyway about 1mb each. but when you
> will apply, say, 'lines' to it - you will get a lazy list of

Actually, in the testing i did, I used lazy bytestrings of 1,2,4,8,16,32
and 64 bytes each. Each with its own ForeignPtr.

> i think that the patch is essential, because small strings (and other
> byte arrays) are much more used than megabyte and gigabyte ones

Yes. Fair enough. I haven't yet seen any stunning improvements (with
small strings), but there's some effect. I'm surprised that the space
usage improvement wasn't more dramatic.  There's definitely some
improvement though.

-- Don