Re: smp: Start up non-boot CPUs asynchronously

[Ingo Molnar <mingo@elte.hu>]

* Arjan van de Ven <arjan@infradead.org> wrote:

> On Tue, 31 Jan 2012 15:31:31 +0100
> Ingo Molnar <mingo@elte.hu> wrote:
> 
> > > 
> > > by inspection, anything that calls 
> > > get_online_cpus()/put_online_cpus() will block while a CPU 
> > > is coming up. This is used in things like 
> > > kmem_cache_create()... which is used about everywhere. 
> > > (there's various other places... more or less it's a 
> > > requirement for using the for_each_online_cpu() api 
> > > correctly)
> > 
> > Still magic delays are not acceptable - we want to face any 
> > remaining performance problems head on, we want to 
> > understand and fix them correctly.
> 
> it's not really a performance problem as it is an obvious "we 
> have a ton of back-to-back writers on a read-write lock that 
> we have quite a few readers for". Unless the writers back off 
> a little, the readers are going to get starved.

I didn't think I'd ever quote Bush, but my reaction to that is: 
'Bring it on!' ;-)

Really, we don't want *more* random delays in kernel code.

Thanks,

	Ingo