linux-kernel - Re: TTM page pool allocator

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Date:	Thu, 23 Jul 2009 00:24:15 +0100
From:	Keith Whitwell <keithw@...are.com>
To:	Jerome Glisse <glisse@...edesktop.org>
Cc:	Thomas Hellström <thomas@...pmail.org>,
	Michel Dänzer <michel@...nzer.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.sf.net" <dri-devel@...ts.sf.net>
Subject: Re: TTM page pool allocator

On Wed, 2009-07-22 at 15:35 -0700, Jerome Glisse wrote:
> On Wed, 2009-07-22 at 21:13 +0200, Thomas Hellström wrote:
> > Jerome Glisse wrote:
> > > On Wed, 2009-07-22 at 15:16 +0200, Michel Dänzer wrote:
> > >   
> > >> On Tue, 2009-07-21 at 21:22 +0200, Jerome Glisse wrote:
> > >>     
> > >>> On Tue, 2009-07-21 at 20:00 +0200, Jerome Glisse wrote:
> > >>>       
> > >>>> On Tue, 2009-07-21 at 19:34 +0200, Jerome Glisse wrote:
> > >>>>         
> > >>>>> On Thu, 2009-06-25 at 17:53 +0200, Thomas Hellström wrote:
> > >>>>>           
> > >>>>>> 4) We could now skip the ttm_tt_populate() in ttm_tt_set_caching, since 
> > >>>>>> it will always allocate cached pages and then transition them.
> > >>>>>>
> > >>>>>>             
> > >>>>> Okay 4) is bad, what happens (my brain is a bit meltdown so i might be
> > >>>>> wrong) :
> > >>>>> 1 - bo get allocated tt->state = unpopulated
> > >>>>> 2 - bo is mapped few page are faulted tt->state = unpopulated
> > >>>>> 3 - bo is cache transitioned but tt->state == unpopulated but
> > >>>>>     they are page which have been touch by the cpu so we need
> > >>>>>     to clflush them and transition them, this never happen if
> > >>>>>     we don't call ttm_tt_populate and proceed with the remaining
> > >>>>>     of the cache transitioning functions
> > >>>>>
> > >>>>> As a workaround i will try to go through the pages tables and
> > >>>>> transition existing pages. Do you have any idea for a better
> > >>>>> plan ?
> > >>>>>
> > >>>>> Cheers,
> > >>>>> Jerome
> > >>>>>           
> > >>>> My workaround ruin the whole idea of pool allocation what happens
> > >>>> is that most bo get cache transition page per page. My thinking
> > >>>> is that we should do the following:
> > >>>> 	- is there is a least one page allocated then fully populate
> > >>>> 	the object and do cache transition on all the pages.
> > >>>> 	- otherwise update caching_state and leaves object unpopulated
> > >>>>
> > >>>> This needs that we some how reflect the fact that there is at least
> > >>>> one page allocated, i am thinking to adding a new state for that :
> > >>>> ttm_partialy_populated
> > >>>>
> > >>>> Thomas what do you think about that ?
> > >>>>
> > >>>> Cheers,
> > >>>> Jerome
> > >>>>         
> > >>> Attached updated patch it doesn't introduce ttm_partialy_populated
> > >>> but keep the populate call in cache transition. So far it seems to
> > >>> work properly on AGP platform
> > >>>       
> > >> Yeah, this one works for me as well.
> > >>
> > >>     
> > >>> and helps quite a lot with performances.
> > >>>       
> > >> Can't say I've noticed that however. How did you measure?
> > >>     
> > >
> > > gears 
> > Hmm,
> > In gears there shouldn't really be any buffer allocation / freeing going 
> > on at all once the display lists are set up, and gears should really be 
> > gpu bound in most cases.
> > 
> > what's the source of the buffer allocations / frees when gears is run?
> > 
> > /Thomas
> 
> We free reallocate vertex buffer each frame iirc.

Gears does everything in display lists which means geometry is held in
VBOs retained for the life of the application.  Once the first frame is
rendered there shouldn't be any more uploads.

Keith

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