Re: [RFC 00/15] x86_64: Optimize percpu accesses

[Ingo Molnar]

* Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote:

> Mike Travis <travis@xxxxxxx> writes:
> 
> 
> > The biggest growth came from moving all the xxx[NR_CPUS] arrays into 
> > the per cpu area.  So you free up a huge amount of unused memory 
> > when the NR_CPUS count starts getting into the ozone layer.  4k now, 
> > 16k real soon now, ??? future?
> 
> Hmm.  Do you know how big a role kernel_stat plays.
> 
> It is a per cpu structure that is sized via NR_IRQS.  NR_IRQS is by 
> NR_CPUS. So ultimately the amount of memory take up is 
> NR_CPUS*NR_CPUS*32 or so.
> 
> I have a patch I wrote long ago, that addresses that specific nasty 
> configuration by moving the per cpu irq counters into pointer 
> available from struct irq_desc.
> 
> The next step which I did not get to (but is interesting from a 
> scaling perspective) was to start dynamically allocating the irq 
> structures.

/me willing to test & babysit any test-patch in that area ...

this is a big problem and it's getting worse quadratically ;-)

	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/