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Subject: Re: SG14 Features
From: Patrice Roy (patricer_at_[hidden])
Date: 2019-12-11 15:26:44


During the SG14 meeting, I was with a friend from one of the major game
companies in Montréal, and he provided me with an interesting list. It will
take me a few days to organize something but I'll publish it here soon.

Le mer. 11 déc. 2019 à 16:24, Jeremy Ong via SG14 <sg14_at_[hidden]> a
écrit :

> This is a bit out of left field, but I'd be interested in a data structure
> adapter which packs its elements based on Morton codes (or some other
> space-filling Hilbert curve, see
> https://en.wikipedia.org/wiki/Z-order_curve).
>
> The idea is that there are a good chunk of algorithms that operate on
> densely packed structures where the likelihood of accessing neighboring
> elements is high. Examples I can think of off the top of my head:
> 1. Simulating a fluid or crowd motion
> 2. Any finite element model (e.g. simulating cloth)
> 3. Lattice computation (e.g. Lattice quantum chromodynamics)
> 4. Sampling neighboring points in an image, possibly for the purposes of
> compression or filtering
> 5. A painting application (e.g. flood fill, drawing a continuous
> stroke/curve to a raster).
> 6. Accelerating a matrix multiplication by parallelizing the computation
> on minors.
>
> The last application perhaps best captures the "gist" of why this is
> useful. If I want to parallelize my computation, I need to partition the
> data in contiguous chunks. Otherwise, each thread or worker will ultimately
> be accessing essentially random addresses within the data range. Aside from
> memory coherency issues, this would cause issues with false sharing if my
> data is not padded to the size of a cache line.
>
> This technique is widely used already in GPUs. For example, when uploading
> a texture for sampling later on, if the texture isn't already
> block-compressed, the GPU will swizzle the texture such that sampling is
> efficient. For the purposes of bilinear filtering, neighboring pixels will
> fetch 4 texels in the texture that will all likely reside in the texture
> cache. If not, they generally can be populated in the cache with a single
> cache-line load (as opposed to four).
>
> This could be implemented in user-land (e.g. `std::nd_array<typename T,
> size_t...>` ignore the bad name for the time-being) in an arbitrary number
> of dimensions. The tradeoff is that single element access will require
> several cycles to compute the address (a few bit operations).
>
> Does this warrant inclusion in the standard? This is actually something
> not 100% clear to me but I'd be interested in other people's thoughts.
>
> On Wed, Dec 11, 2019 at 1:45 PM Matthew Butler via SG14 <
> sg14_at_[hidden]> wrote:
>
>> I would be interested in hearing everyone's thoughts on Herbceptions.
>>
>> Also Colony and Ring Buffer would be useful adds.
>>
>> On Wed, Dec 11, 2019 at 1:41 PM Tjernstrom, Staffan via SG14 <
>> sg14_at_[hidden]> wrote:
>>
>>> Today's call discussed informally which features we would like to pursue
>>> as a group for '23 and beyond. Many suggestions appeared both in the chat
>>> as well as in the call itself.
>>>
>>>
>>>
>>> Feel free to use this thread as a collection point that we can circle
>>> back around to and gather inspiration from.
>>>
>>>
>>>
>>> Kind Rgds
>>>
>>> Staffan Tj.
>>>
>>>
>>>
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