[PATCH v3] faster strlen on x64

[Ondřej Bílka]

On Wed, Feb 06, 2013 at 11:18:06AM -0500, Carlos O'Donell wrote:
> On 02/05/2013 06:44 PM, Ondřej Bílka wrote:
> > My implementation takes profiling information (see http://kam.mff.cuni.cz/~ondra/benchmark_string/profile/result.html for my workload.)
> > into account. Important property there is that most strings are at most
> > 80 bytes large.
> 
> I think this information is really important.
> 
> How did you profile this?
> 
I use two tools that do profiling. I generated these statistics with 
https://github.com/neleai/benchmark_string directory profile.
It is in hacky state with several problems, it has relatively big 
constant overhead when writing results. I do not use it to collect 
timing information. Also malloc profiling is not entirely stable.

I based on it http://kam.mff.cuni.cz/~ondra/strlen_profile.tar.bz2
that compares strlen only and can measure time with minimal overhead. 

To use it
Download profiler at http://kam.mff.cuni.cz/~ondra/strlen_profile.tar.bz2
run make

This compiles it and displays usage information.
I collect information on everything that I run by adding

LD_PRELOAD=displayed directory
export LD_PRELOAD

into .bashrc

To generate results directory from collected data run 
make rep
To zero data run 
make reset

> I see that your workload is ~10 applications.
> 
This is technical limitation that I use fixed array with top 10 entries.

> Can another user run this to get their statistics?
As above.
> 
> Cheers,
> Carlos.