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

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Date:	Fri, 14 Sep 2012 12:51:53 +0000
From:	"Deucher, Alexander" <Alexander.Deucher@....com>
To:	Christian König <deathsimple@...afone.de>,
	Jerome Glisse <j.glisse@...il.com>
CC:	Alex Deucher <alexdeucher@...il.com>,
	"Cherkasov, Dmitrii" <Dmitrii.Cherkasov@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	Dave Airlie <airlied@...hat.com>,
	Dmitry Cherkasov <dcherkassov@...il.com>
Subject: RE: [PATCH] Add 2-level GPUVM pagetables support to radeon driver.

> -----Original Message-----
> From: Christian König [mailto:deathsimple@...afone.de]
> Sent: Friday, September 14, 2012 4:49 AM
> To: Jerome Glisse
> Cc: Alex Deucher; Cherkasov, Dmitrii; linux-kernel@...r.kernel.org; dri-
> devel@...ts.freedesktop.org; Deucher, Alexander; Dave Airlie; Dmitry
> Cherkasov
> 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...

It's LOG2:

PAGE_TABLE_BLOCK_SIZE 	27:24 	0x0 	log2 number of pages in page table block (default = 1 page)

> 
> Christian.


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