linux-kernel - Re: TTM page pool allocator

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Date:	Fri, 26 Jun 2009 09:31:55 +0200
From:	Jerome Glisse <glisse@...edesktop.org>
To:	Dave Airlie <airlied@...il.com>
Cc:	thomas@...pmail.org, linux-kernel@...r.kernel.org,
	dri-devel@...ts.sf.net
Subject: Re: TTM page pool allocator

On Fri, 2009-06-26 at 10:00 +1000, Dave Airlie wrote:
> On Thu, Jun 25, 2009 at 10:01 PM, Jerome Glisse<glisse@...edesktop.org> 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.
> 

I think it's better to fix userspace to not allocate as much buffer per
frame as it does now rather than having a pool of wb pages, i removed
it because on my 64M box memory is getting tight, we need to compute
the number of page we still based on memory. Also i think it's ok
to assume that page allocation is fast enough.

I am reworking the patch with lastes Thomas comment, will post new one
after a bit of testing.

Cheers,
Jerome

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