CPU consumption is going as high as 95% on ARM Cortex A8

[Hiremath, Vaibhav]

> -----Original Message-----
> From: Russell King - ARM Linux [mailto:linux at arm.linux.org.uk]
> Sent: Monday, December 21, 2009 2:38 PM
> To: Hiremath, Vaibhav
> Cc: linux-arm-kernel at lists.infradead.org; linux-mm at kvack.org; linux-
> omap at vger.kernel.org
> Subject: Re: CPU consumption is going as high as 95% on ARM Cortex
> A8
> 
> On Mon, Dec 21, 2009 at 11:56:23AM +0530, Hiremath, Vaibhav wrote:
> > >         vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
> > >
> > > will result in the memory being mapped as 'Strongly Ordered',
> > > resulting
> > > in there being multiple mappings with differing types.  In later
> > > kernels, we have pgprot_dmacoherent() and I'd suggest changing
> the
> > > above
> > > macro for that.
> > >
> >
> > I tried with your suggestion above but unfortunately it didn't
> work for
> > me. I am seeing the same behavior with the pgprot_dmacoherent(). I
> > pulled your patch (which got applied cleanly on 2.6.32-rc5) -
> 
> What happens if you comment out the pgprot_dmacoherent() /
> pgprot_noncached()
> line completely?
> 
[Hiremath, Vaibhav] If I comment the line completely then I am seeing CPU consumption similar to when I was setting PAGE_READONLY/PAGE_SHARED flag, which is 25-32%.

Thanks,
Vaibhav

> I suspect that will "solve" the problem - but you'll then no longer
> have
> DMA coherency with userspace, so its not really a solution.