Re: 2048 CPUs [was: Re: New filesystem for Linux]

[Pavel Machek <pavel@ucw.cz>]

Hi!

> >The SGI Altix can have 2048 CPUs.
> 
> And does it run one image of Linux? Or more images each 
> on few cpus?
> 
> How do they solve problem with spinlock livelocks?
> 
> If time-spent-outside-spinlock/time-spent-in-spinlock < 
> number-of-cpus, the spinlock livelock may happen --- 
> this condition is not true normally with 2 or 4 cpus, 
> but for that high amount of cpus, there is a danger.

Lets say time-spent-outside-spinlock == time-spent-in-spinlock and
number-of-cpus == 2.

1 < 2 , so it should livelock according to you...

...but afaict this should work okay. Even if spinlocks are very
unfair, as long as time-outside and time-inside comes in big chunks,
it should work.

If you are unlucky, one cpu may stall for a while, but... I see no
livelock.

-- 
Thanks for all the (sleeping) penguins.