linux-kernel - Re: TTM page pool allocator

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Date:	Fri, 26 Jun 2009 08:31:37 +0200
From:	Thomas Hellström <thomas@...pmail.org>
To:	Dave Airlie <airlied@...il.com>
CC:	Jerome Glisse <glisse@...edesktop.org>,
	linux-kernel@...r.kernel.org, dri-devel@...ts.sf.net
Subject: Re: TTM page pool allocator

Dave Airlie skrev:
> 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.
>   

Yes, I think in the latter case the user-space driver should take care 
to specify WC from the beginning, when the BO is allocated.

BTW is there any DMA buffer verification taking place on WC buffers on 
Radeon?

> Dave.
>   

/Thomas

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