linux-kernel - Re: [PATCH] Add 2-level GPUVM pagetables support to radeon driver.

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Message-ID: <5052EF8F.1020905@vodafone.de>
Date:	Fri, 14 Sep 2012 10:49:19 +0200
From:	Christian König <deathsimple@...afone.de>
To:	Jerome Glisse <j.glisse@...il.com>
CC:	Alex Deucher <alexdeucher@...il.com>,
	Dmitry Cherkasov <Dmitrii.Cherkasov@....com>,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	Alex Deucher <alexander.deucher@....com>,
	Dave Airlie <airlied@...hat.com>,
	Dmitry Cherkasov <dcherkassov@...il.com>
Subject: Re: [PATCH] Add 2-level GPUVM pagetables support to radeon driver.

On 13.09.2012 20:42, Jerome Glisse wrote:
> On Thu, Sep 13, 2012 at 2:37 PM, Alex Deucher <alexdeucher@...il.com> wrote:
>> On Thu, Sep 13, 2012 at 2:17 PM, Jerome Glisse <j.glisse@...il.com> wrote:
>>> On Thu, Sep 13, 2012 at 10:13 AM, Dmitry Cherkasov
>>> <dcherkassov@...il.com> wrote:
>>>> PDE/PTE update code uses CP ring for memory writes.
>>>> All page table entries are preallocated for now in alloc_pt().
>>>>
>>>> It is made as whole because it's hard to divide it to several patches
>>>> that compile and doesn't break anything being applied separately.
>>>>
>>>> Tested on cayman card.
>>>>
>>>> Signed-off-by: Dmitry Cherkasov <Dmitrii.Cherkasov@....com>
>>>> ---
>>>> I couldn't test in on SI card, so would be happy if someone could check it there.
>>> I wonder how this could have work as you don't set
>>> PAGE_TABLE_BLOCK_SIZE field so each page directory entry cover only 1
>>> page.
>> I think PAGE_TABLE_BLOCK_SIZE refers number of 4k pages used for PTE
>> entries per PDE.  E.g., 1 4k page contains 512 64 bit PTEs. so if
>> BLOCK_SIZE is set to 1 page, each PDE points to 1 page (4k) or PTE
>> entries.  If BLOCK_SIZE is 2, each PDE points to 2 pages (8k) or PTEs,
>> etc.
>>
>> Alex
>>
> If so then it's ok
Yeah, minor nitpick: BLOCK_SIZE seems to be number of 4k pages in a page 
directory entry minus 1.

So with a BLOCK_SIZE of 0 you get one 4K page and with a BLOCK_SIZE of 1 
you get 8K, etc...

Christian.
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