Re: benh performance problem

On Feb 5, 2004, at 11:14 PM, Benjamin Herrenschmidt wrote:

On Thu, 2004-02-05 at 21:09, Mikolaj Krzewicki wrote:

quoted

2.6.1-benh1, HZ=1000: timing=36.5s
2.6.1-benh1, HZ=100 : timing=32s

The fact that pbbuttons makes a difference makes me think the
interrupt handling is taking way too much time on your setup,
and pbbuttons is loading the machine with PMU interrupts...

pbbuttons is loading the machine? What about all those extra
decrementer ticks? I assume benchmarks showed no performance
degradation on some class of ppc32; what was the slowest system tested?
For that matter, couldn't this hurt 4xx, 8xx(x), as well?

Perhaps HZ should be user-configurable? Although that doesn't help
distributions who'd like one kernel to work everywhere... How does
Linux handle increased HZ on old i386 anyways?

Not sure if I can fix any of this at this point without doing a
major rewrite of the exception handling code, I suspect those
CPUs don't like running in real mode and our exception handling
happens mostly in that mode in ppc32...

I didn't realize CPUs go slower in real mode..?

--
Hollis Blanchard
IBM Linux Technology Center


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