PID Allocator Performance Results (was: Re: [UPDATE] new pid alloc...)

[John Baldwin]

On Sunday 08 February 2004 04:49 am, Poul-Henning Kamp wrote:
> In message <20040208094537.GA14749 at VARK.homeunix.com>, David Schultz writes:
> >> 10nsec per operation is getting you into the territory of effective
> >> TSC-timecounter resolution, RAM access time, cache miss delays
> >> and all sorts of other hardware effects.
> >
> >To avoid jitter and timestamping overhead, I read the time only at
> >the start and end of the entire sequence of 10000 operations.
> >I obtained the sample variance by running the entire test three
> >times, i.e.
>
> Yes, but you have to remember that quite a lot of stuff happens
> in the kernel of your iteration, and the stratification seems
> to happen there.
>
> >Nevertheless, you're definitely right about the stratification.
> >
> >Yes, I realize that.  I took 10 more samples of 10000 forks each
> >with 5000 sleeping processes in the background and got the
> >following:
> >
> >This data show a difference at the 95% confidence level, namely,
> >that the NetBSD algorithm is about 1% faster on a system with 5000
> >processes (and only 0.1% faster if you're looking at the total
> >overhead of fork() rather than vfork().)  I think that pretty much
> >rules out performance as the deciding factor between the two.
>
> Uhm, if you are using "Student's T" you have to remember that it
> is only valid for gaussian noise processes.  The stratification
> we see is not any where near to gaussian.
>
> Either way:  "tjr" should be our choice.

Agreed.  I'll defer to das@ on this one as he is the one who has done the 
actual research.  Tom's version certainly seems to be the consensus.

-- 
John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org