Re: [9fans] interesting timing tests

[erik quanstrom <quanstro@quanstro.net>]

> Is there a way to check this?
>
> Is there a way to completely shut off N processors and
> measure benchmark speed slow down as function of processor?

there hasn't been any performance impact measured.
however, the extreme system time still seems wierd.

richard miller suggested that kprof might be suffering from sampleing
error, and moving rebalance to the end of the file confirmed.  both
the 4- and 16- processor machines have similar behavior.

> > the underlying assumption is that the contended case is rare.
> > if this is not the case, then spin locks are not a good choice.
>
> With 8 dual HT processors the probability has gone up quite a
> bit!

only if contention depends on processing speed.  (locks may be
interrupted if they're not ilocks.)

for example, a lock protecting packet rx for an ethernet
driver would not depend strongly on the number of processors or
processing speed.

> And what will you replace spinlocks with?

the right answer here is likely "mu".  some spinlocks
might need to be replaced with another structure.
but i would think that would depend entirely on the
situation.  in general, i am not suggesting
depricating spinlocks.

- erik