[linux-mm-cc] [RFC] LZO de/compression support - take 6

[Nitin Gupta]

On 5/28/07, Adrian Bunk <bunk at stusta.de> wrote:
> On Mon, May 28, 2007 at 08:10:31PM +0530, Nitin Gupta wrote:
> > Hi,
> >
> > Attached is tester code used for testing.
> > (developed by Daniel Hazelton -- modified slightly to now use 'take 6'
> > version for 'TinyLZO')
> >
> > Cheers,
> > Nitin
> >
> > On 5/28/07, Nitin Gupta <nitingupta910 at gmail.com> wrote:
> >> (Using tester program from Daniel)
> >>
> >> Following compares this kernel port ('take 6') vs original miniLZO code:
> >>
> >> 'TinyLZO' refers to this kernel port.
> >>
> >> 10000 run averages:
> >> 'Tiny LZO':
> >>        Combined: 61.2223 usec
> >>        Compression: 41.8412 usec
> >>        Decompression: 19.3811 usec
> >> 'miniLZO':
> >>        Combined: 66.0444 usec
> >>        Compression: 46.6323 usec
> >>        Decompression: 19.4121 usec
> >>
> >> Result:
> >> Overall: TinyLZO is 7.3% faster
> >> Compressor: TinyLZO is 10.2% faster
> >> Decompressor: TinyLZO is 0.15% faster
>

> So your the compressor of your version runs 10.2% faster than the
> original version.
>
> That's a huge difference.
>
> Why exactly is it that much faster?
>
> cu
> Adrian

I am not sure on how to account for this _big_ perf. gain but from
benchmarks I see that whenever I remove unncessary casting from tight
loops I get perf. gain of 1-2%. For e.g. open coding
LZO_CHECK_MPOS_NON_DET macro with all unnecessary casting removed,
gave perf. gain of ~2%. Similarly, I found many other places where
such casting was unnecessary.

These changes have been tested on x86, amd64, ppc. Testing of 'take 6'
version is yet to be done - this will confirm that I didn't
reintroduce some error.

- Nitin