linux-kernel - Re: TTM page pool allocator

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Date:	Mon, 29 Jun 2009 23:12:02 +0200
From:	Thomas Hellström <thomas@...pmail.org>
To:	Jerome Glisse <glisse@...edesktop.org>
CC:	Dave Airlie <airlied@...il.com>, linux-kernel@...r.kernel.org,
	dri-devel@...ts.sf.net
Subject: Re: TTM page pool allocator

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@...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.
>> --
>>     
>
> 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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