Re: TTM page pool allocator

[Thomas Hellström]

Jerome Glisse skrev:
> On Fri, 2009-06-26 at 10:00 +1000, Dave Airlie wrote:
>   
> > On Thu, Jun 25, 2009 at 10:01 PM, Jerome Glisse<glisse@xxxxxxxxxxxxxxx> wrote:
> >     
> > > Hi,
> > >
> > > Thomas i attach a reworked page pool allocator based on Dave works,
> > > this one should be ok with ttm cache status tracking. It definitely
> > > helps on AGP system, now the bottleneck is in mesa vertex's dma
> > > allocation.
> > >
> > >       
> > My original version kept a list of wb pages as well, this proved to be
> > quite a useful
> > optimisation on my test systems when I implemented it, without it I
> > was spending ~20%
> > of my CPU in getting free pages, granted I always used WB pages on
> > PCIE/IGP systems.
> >
> > Another optimisation I made at the time was around the populate call,
> > (not sure if this
> > is what still happens):
> >
> > Allocate a 64K local BO for DMA object.
> > Write into the first 5 pages from userspace - get WB pages.
> > Bind to GART, swap those 5 pages to WC + flush.
> > Then populate the rest with WC pages from the list.
> >
> > Granted I think allocating WC in the first place from the pool might
> > work just as well since most of the DMA buffers are write only.
> >
> > Dave.
> > --
> >     
>
> Attached a new version of the patch, which integrate changes discussed.
>
> Cheers,
> Jerome
>   
Hi, Jerome!
Still some outstanding things:

1) The AGP protection fixes compilation errors when AGP is not enabled, 
but what about architectures that need the map_page_into_agp() semantics 
for TTM even when AGP is not enabled? At the very least TTM should be 
disabled on those architectures. The best option would be to make those 
calls non-agp specific.

2) Why is the page refcount upped with get_page() after an alloc_page()?

3) It seems like pages are cache-transitioned one-by-one when freed. 
Again, this is a global TLB flush per page. Can't we free a large chunk 
of pages at once?

/Thanks,
Thomas






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