Testing box available.

Kris Kennaway kris at FreeBSD.org
Thu Feb 14 10:36:36 UTC 2008

Julian Elischer wrote:

> my memory is that ohk changed make to have a fifo with N (as in -j N)
> tokens in it and all child makes inherrit this fifo
> (or get it's name from an environment variable or something)
> and can only spawn extra makes if they can get a token.
> When they have finished their work they pu the token back into the
> fifo..
> My memories of this may be somewhat inaccurate however.

I think this is correct but it only helps to some extent.  Large parts 
of the buildworld have no or low parallelism still (e.g. the whole 'make 
depend' phase).

'make buildworld' is not a good choice for testing parallelism.  Running 
a "useful workload" is more interesting :)  One of three things will happen:

1) It may scale well to 16 CPUs.

2) The scheduler may limit performance if your workload depends heavily 
on CPU locality.  This is the case with the Intel 16-core system we have 
been using.  The scheduler needs to gain knowledge of the CPU core 
topology in order to avoid making bad decisions about migrating 
processes between CPU cores that are far apart.  Jeff is working on this.

3) Your workload may not scale because of a limiting factor in userland 
or in the kernel.  If this is a limitation in FreeBSD and not the 
application then it is interesting.

Actually it would be interesting to repeat some of our "standard tests" 
on the barcelona system to see how it compares to the intel one.


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