[fpc-devel] make -j for windows, number of cores?

Mark Morgan Lloyd markMLl.fpc-devel at telemetry.co.uk
Mon Mar 17 11:08:10 CET 2014

Reinier Olislagers wrote:

> Quick test on Linux x64 VM seems to show increasing to 8 (matching my #
> of physical cores, no hyperthreading on my CPU) does increase
> performance... using the famous unit of time called "number of cups of
> coffee I thought I drank while waiting for the compile"

Historically, 8 has been a bit of a limit on many different 
architectures. I don't know where this figure has come from, ultimately 
it could be something like a speed ratio between main memory devices and 
cache. Some of the larger systems have attempted to get round this limit 
by having multiple busses, e.g. 4x on the Cray CS6400 which was a 
precursor of the Sun E10K.

My tests suggest that the shape of the rolloff is OS-specific. IBM 
mainframes, of course, claim to vastly exceed anybody else's throughput, 
but I believe that they've got things like four-level cache as well as 
fibre-connected NUMA.

Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk

[Opinions above are the author's, not those of his employers or colleagues]

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