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- From: "Bo Huang" <
>
- To: <
>
- Subject: [Manta] RE: Re: Re: Re: Re: information about the acceleration structures?
- Date: Mon, 12 Apr 2010 14:41:45 -0400
It seems RecursiveGrid is the better choice than DynBVH for path tracing due
to incoherence. As for Manta's path tracer implementation where the
RayPacketData is constantly sorted to be material coherent, can I assume
RecursiveGrid is still better because sorting or not, the directions taken by
the rays are still incoherent due to varying pdfs.
Regarding the more solid performance achieved by Manta's standard ray tracer
compared to the GPU version, would any path tracer comparison be similar? The
intensive sorting of RayPacketData mentioned frequently yields sub-packets
with length <5 for example, and I wonder if any tricks GPU developers may
employ. Of course, I am also curious in general what Manta's path tracer
excels or lacks, other than the ones I mentioned in a thread a while back.
For example, on the CPU, is sorting still better than single ray traversal in
Manta's path tracer.
What are some reasons the gain made by BSP is miniscule compared to others
assuming geometries are static?
Why does reducing packet size (default is 64) influence DynBVH?
Thanks
Bo
-----Original Message-----
From: Thiago Ize
[mailto:
Sent: Sun 4/11/2010 4:21 PM
To:
Cc: Carson Brownlee
Subject: [Manta] Re: Re: Re: Re: information about the acceleration
structures?
Packet size should be an issue for certain acceleration structures when
you have lots of triangles or incoherent rays, such as in path tracing.
If the structure only traces a single ray at a time, then this clearly
doesn't matter much, nor does it matter too much if the acceleration
structure can gracefully degenerate to a single ray type of performance,
which DynBVH can sort of do in some situations (although the state of
the art in this has improved since DynBVH was written). Some
structures, like the kdtree, do not handle large packets well when each
ray wants to traverse different nodes and so in this case smaller
packets or even an explicit single ray traversal might work better.
I'm not familiar with GridSpheres, but I would assume that RecursiveGrid
would be a much better grid structure than that. RecursiveGrid has the
nice property that it scales to really large number of primitives in
both performance and while using only linear memory and offering decent
traversal performance for a single ray traversal algorithm. Note that
the build is not at all optimized so it can be a bit slow.
While you mentioned manta performance compared to gpu rasterizer
performance, in the case of gpu ray tracing performance I've come across
some interesting results. I've done some light benchmarking of manta
running on a nice system (8 nehalem cores) versus a GPU only ray tracer
(NVIDIA's Optix) running on a tesla s870 (4 GPUs for total of 2TFlops of
performance) all on the same system and found that manta was about 20%
faster in all my tests and could scale up to large datasets since it was
not restricted to a tiny amount of GPU memory. Of course, you can now
get a tesla system that is twice as fast, but the same also goes for the
CPUs (plus manta has access to all of the cheap system memory versus the
small expensive memory restrictions of GPUs). The take home message is
that Manta should be pretty fast if you can run it using SSE and on a
machine with many cores. That of course is the important point. If you
have a really fancy and expensive graphics card(s) and run manta on a 2
core machine with SSE turned off, then of course manta won't stand a
chance.
Thiago
David E DeMarle wrote:
>
I'll try to post a better (but still informal) breakdown to the manta list
>
later this week. Here is a sketch of what performance looks like to
>
me:
>
>
The timings are for the MantaBenchmark program in vtkManta that I
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wrote, I will export the data to something pure manta can read and
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see how that compares this week.
>
>
The best accel structure in my benchmark is DynBVH. With that starting
>
around 50k triangles the framerate starts to plummet downward from
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60fps to 30fps at 100k to 6fps at 1million. Playing with max packet
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size changes the 1million tri case by about 1fps on either side.
>
>
GridSpheres 3 is better between 50k and 100k (it drops barely at all),
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but shortly after 100k the build runs out of memory and crashes. The
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build time is too long to use in practice for sci-vis, where change is
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the norm and pure rendering (just camera motion) comes in bursts.
>
>
Manta pretty handily outperforms Mesa GL (it is roughly even for < 50k
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and against a single manta thread), but it never outperforms GL on my
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NVidia card. It does start to be competative above 1million tris though.
>
>
David E DeMarle
>
Kitware, Inc.
>
R&D Engineer
>
28 Corporate Drive
>
Clifton Park, NY 12065-8662
>
Phone: 518-371-3971 x109
>
>
>
>
On Sun, Apr 11, 2010 at 3:34 AM, Carson Brownlee
>
<
>
>
wrote:
>
>
> How many triangles are you talking about and would you mind giving a
>
> breakdown of your timings? I believe Thiagos comment on decreasing packet
>
> size may help if you have a small window size and lot of threads which
>
> might
>
> choke the load balancer. It should not affect single threaded performance
>
> however.
>
> Carson
>
>
>
>
>
> On Apr 9, 2010, at 5:35 PM, David E DeMarle wrote:
>
>
>
>
>
>> Awesome, thanks.
>
>>
>
>> David E DeMarle
>
>> Kitware, Inc.
>
>> R&D Engineer
>
>> 28 Corporate Drive
>
>> Clifton Park, NY 12065-8662
>
>> Phone: 518-371-3971 x109
>
>>
>
>>
>
>>
>
>> On Fri, Apr 9, 2010 at 7:30 PM, Thiago Ize
>
>> <
>
>
>> wrote:
>
>>
>
>>> BSP and CellSkipper you probably would never want to use since the BSP
>
>>> has a
>
>>> super slow build for relatively minor speed gains and CellSkipper is slow
>
>>> and just interesting from an academic view.
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>>>
>
>>> RecursiveGrid is a very good choice when the rays are very incoherent and
>
>>> single ray traversal is just as good (or better) than packet traversal.
>
>>> This happens with path tracing for instance. The number of levels to
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>>> use
>
>>> is described in my dissertation, but 3 is usually the right amount. The
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>>> build is decent, but could be made much faster if someone spent the time
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>>> to
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>>> optimize it.
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>>>
>
>>> KDTree is ok, but the version in manta is not as optimized as it could
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>>> be,
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>>> so I'd probably use DynBVH over it.
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>>>
>
>>> DynBVH is usually a good acceleration structure to use. The build can be
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>>> made faster by going into cmake and turning
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>>> MANTA_USE_DYNBVH_APPROXIMATE to ON
>
>>> however that will result in slower traversal performance. Faster build
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>>> algorithms exist and someone should implement it as well as parallelizing
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>>> the build.
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>>>
>
>>> The poor scaling with increasing triangles could be a result of the
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>>> packet
>
>>> size being too big. Trying turning it down to see if it improves
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>>> performance. The exception to this rule is RecursiveGrid which already
>
>>> does
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>>> a single ray traversal so packet size is not an issue.
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>>>
>
>>> If possible, I'd recommend flattening the groups so that there is just a
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>>> single group and then building a tree over this since this will give the
>
>>> best performance. Otherwise, the type of structures to use would depend
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>>> on
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>>> how the objects are distributed within a group and how the groups are
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>>> distributed.
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>>>
>
>>> Thiago
>
>>>
>
>>> David E DeMarle wrote:
>
>>>
>
>>>> Can anyone tell me about, or point me to descriptions of, the ?five?
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>>>> different acceleration structures (BSP, CellSkipper, RecursiveGrid,
>
>>>> KDTree, RecursiveGrid) in Manta?
>
>>>>
>
>>>> vtkManta uses DynBVH, and it appears to be the fastest so far, but it
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>>>> doesn't seem to scale all that well when the number of triangles
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>>>> increases. I am wondering if one of the others (with well chosen
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>>>> settings) would be a better choice.
>
>>>>
>
>>>> So far, vtkManta isn't changing the contents of the DynBVH, so the
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>>>> Dynamic nature of it isn't that important (but quick build times are
>
>>>> important).
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>>>>
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>>>> We do want to be able to have (groups of) triangles, cylinders and
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>>>> spheres in the acceleration structure so a non-homogenous acceleration
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>>>> structure is preferable.
>
>>>>
>
>>>> thanks for any pointers,
>
>>>>
>
>>>> David E DeMarle
>
>>>> Kitware, Inc.
>
>>>> R&D Engineer
>
>>>> 28 Corporate Drive
>
>>>> Clifton Park, NY 12065-8662
>
>>>> Phone: 518-371-3971 x109
>
>>>>
>
>>>>
>
>
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<<winmail.dat>>
- [Manta] Re: Re: Re: Re: information about the acceleration structures?, (continued)
- [Manta] Re: Re: Re: Re: information about the acceleration structures?, Thiago Ize, 04/11/2010
- [Manta] Re: Re: Re: Re: Re: information about the acceleration structures?, David E DeMarle, 04/11/2010
- [Manta] Re: Re: Re: Re: Re: Re: information about the acceleration structures?, Thiago Ize, 04/11/2010
- [Manta] Re: Re: Re: Re: Re: Re: Re: information about the acceleration structures?, David E DeMarle, 04/12/2010
- [Manta] Re: information about the acceleration structures?, Thiago Ize, 04/13/2010
- [Manta] Re: Re: information about the acceleration structures?, David E DeMarle, 04/14/2010
- [Manta] Re: Re: Re: information about the acceleration structures?, Carson Brownlee, 04/14/2010
- [Manta] Re: Re: Re: Re: information about the acceleration structures?, David E DeMarle, 04/14/2010
- [Manta] Re: Re: Re: Re: information about the acceleration structures?, David E DeMarle, 04/14/2010
- [Manta] Re: Re: information about the acceleration structures?, Carson Brownlee, 04/14/2010
[Manta] RE: Re: Re: Re: Re: information about the acceleration structures?, Bo Huang, 04/12/2010
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