Re: [PATCH] (x)memcoll: performance improvement when input is known to be NUL delimited.

[Pádraig Brady]

On 14/03/10 14:24, Bruno Haible wrote:
> Hi Chen,
> 
>> ... it was consistently (as in every run for 20 runs) faster, and thus I've
>> included it in the patch. 
> 
> Thanks. I'll wait for the FSF notification that the legal papers have arrived.

Hi Chen, The copyright stuff is sorted now I presume?

> 
>> This is not what I expected at all, and I'm having a hard time coming up with
>> a reason why this is
> 
> 15 years ago, on a Linux/x86 machine, I could measure CPU performance with
> about 1% precision (with 3 or 5 runs of a program). At the same time, on
> Windows, I got only about 5% precision.
> 
> On SPARC CPUs, sometimes the same program was 30% slower than the previous 
> day.
> So, such platforms were unusable for benchmarking.

lol

> Today, x86 CPUs have additional complexity: multiple CPU cores that fight over
> the memory bus; hyperthreads. The Linux memory management has become more
> complex as well (the kernel actively swapping out some pages). Sometimes 
> you're
> even running inside a virtual machine. I usually can get only about 2% of
> precision nowadays.

That's why I keep my single core laptop for benchmarking.
After a suspend/resume cycle or large memory thrashing
performance can vary quite a bit, but for multiple runs
within a particular session, it's quite stable.

cheers,
Pádraig.