A page fault causes exiting from WFI mode for all idling cores?

[Catalin Marinas]

On Thu, Jun 02, 2011 at 12:16:57AM +0100, heechul Yun wrote:
> On Wed, Jun 1, 2011 at 5:55 AM, Lorenzo Pieralisi
> <lorenzo.pieralisi at arm.com> wrote:
> > On Wed, 2011-06-01 at 11:14 +0100, Catalin Marinas wrote:
> >> On 28 May 2011 12:59, heechul Yun <heechul at illinois.edu> wrote:
> >> > While I was investigating page fault handling performance on a quad
> >> > core Cortex-A9 ARM processor, I noticed that whenever there is a
> >> > page fault, all idling cores also awakened---exiting from WFI instruction
> >> > on the idle loop (and go back to WFI again).
> >> >
> >> > Since the page fault generating program is running on a single core,
> >> > it seems unnecessary to wake up other idling cores (hence saving
> >> > power) as well.
> >> >
> >> > Can anyone tell me if this, exiting from WFI on every page fault, is
> >> > correct behavior? If so, why?
...
> >> Also note that WFI is just a hint to the processor, so it could get
> >> out of it at any time. Maybe the A9 just does this when it gets some
> >> TLB ops from another CPU.
> >>
> >
> > According to A9 TRM transition from standby to run mode can be triggered
> > by cp15 maintenance requests generated by another cpu, just to reiterate
> > Catalin's reply.
> 
> You mean cache/tlb operations can automatically generate maintenance
> request to other cores (not via IPIs) ?

Yes, starting with Cortex-A9. Without this feature we struggle a bit on
ARM11MPCore where we have to broadcast TLB ops via IPI and do some weird
tricks for cache maintenance (like read for ownership).

-- 
Catalin