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Re: mutexes, locks and so on...

On Wed Nov 24 2010 at 12:42:44 -0500, Thor Lancelot Simon wrote:
> On Wed, Nov 24, 2010 at 04:52:38PM +0200, Antti Kantee wrote:
> > Thanks, I'll use your list as a starting point.  One question though:
> > 
> > On Wed Nov 24 2010 at 00:16:37 +0000, Andrew Doran wrote:
> > > - on a static, unchanging source tree.
> > 
> > >From the SSP discussion I have a recollection that can be
> > very jittery, up to the order of 1% per build.  I've never confirmed it
> > myself, though.  Did you notice anything like that?
> There are other issues associated with as a benchmark.
>       * What are you trying to test?  If you're trying to test the
>         efficiency of cache algorithms or the I/O subsystem (including
>         disk sort), for example, you need to test pairs of runs with
>         a cold boot of *ALL INVOLVED HARDWARE* (this includes disk
>         arrays etc) between each.
>         * If SSDs, hybrid disks, or other potentially self-reorganizing
>           media are involved, forget it, you just basically lose.
>         * If you're trying to test everything *but* the cache and I/O
>           subsystem, then you need to use a "warm up" procedure you can
>           have reasonable confidence works, for example always measuring
>           the Nth of N consecutive builds.

Indeed.  Let's start with the low-hanging fruit first -- having some
figures which at least make some sense (e.g. measure second of two builds
in a row) is better than no figures.

>         * It can be hard to construct a system configuration where NetBSD
>           kernel performance is actually the bottleneck and some other
>           hardware limitation is not.  Or where there's only a single
>           bottleneck.

Dunno about NetBSD specifically, but this suggests great differences:

At least I doubt we got dramatically better drivers between 4 and 5.
No idea about other OS performance there.

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