* Chen, Kenneth W <[email protected]> wrote:
> Ingo Molnar wrote on Sunday, April 03, 2005 7:30 AM
> > how close are these numbers to the real worst-case migration costs on
> > that box?
>
> I booted your latest patch on a 4-way SMP box (1.5 GHz, 9MB ia64). This
> is what it produces. I think the estimate is excellent.
>
> [00]: - 10.4(0) 10.4(0) 10.4(0)
> [01]: 10.4(0) - 10.4(0) 10.4(0)
> [02]: 10.4(0) 10.4(0) - 10.4(0)
> [03]: 10.4(0) 10.4(0) 10.4(0) -
> ---------------------
> cacheflush times [1]: 10.4 (10448800)
great! How long does the benchmark take (hours?), and is there any way
to speed up the benchmarking (without hurting accuracy), so that
multiple migration-cost settings could be tried? Would it be possible to
try a few other values via the migration_factor boot option, in 0.5 msec
steps or so, to find the current sweet spot? It used to be at 11 msec
previously, correct? E.g. migration_factor=105 will change the cost to
10.9 msec, migration_factor=110 will change it to 11.4, etc. Or with the
latest snapshot you can set absolute values as well,
migration_cost=11500 sets the cost to 11.5 msec.
> One other minor thing: when booting a numa kernel on smp box, there is
> a numa scheduler domain at the top level and cache_hot_time will be
> set to 0 in that case on smp box. Though this will be a mutt point
> with recent patch from Suresh Siddha for removing the extra bogus
> scheduler domains.
> http://marc.theaimsgroup.com/?t=111240208000001&r=1&w=2
at first sight the dummy domain should not be a problem, the ->cache_hot
values are only used when deciding whether a task should migrate to a
parallel domain or not - if there's an extra highlevel domain instance
then such decisions are never made, so a zero value makes no difference.
Ingo
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