powerpc kernel flavour

[Jeremy Kerr]

Hi all,

Last UDS, we discussed the possibility of dropping the -powerpc kernel 
flavour, as the powerpc-smp kernel will support the same set of machines, and 
means one less flavour to build.

The potential downside of this is that we lose some optimisations for 
uniprocessor machines; for example, spinlocks will not be compiled-out, as can 
be done with the UP kernel.

I've done some brief benchmarking using sysbench's 'thread' test:

	sysbench --max-requests=100000 --num-threads=64 \
		 --test=threads --thread-yields=100 --thread-locks=2 run


On my g4 machine, I see a 3.5% performance degradation when using the powerpc-
smp flavour (which is statistically significant). However, this is a kernel-
heavy benchmark; we may not see such a change on real workloads. I'm not using 
kernbench as this would be very much disk-bound on this machine.

So, it boils down to: do we care about this 3.5% enough to keep the powerpc 
flavour around?

Cheers,


Jeremy