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How does a mobile GPU work? [pdf]

172 points by goranmoomin 3y ago

anshumankmr 3y ago
I kind of got a reality check reading a Quora answer back in the day when I was hunting for GTA V on Android. There were a lot of scammy terrible apps (and still are).
amelius 3y ago
You can also ask your GPU how it works and to generate the explanation in manga style.
lxgr 3y ago
What's the "conveyor belt" between vertex and fragment shader? Doesn't communication between these two shaders happen via GPU memory in discrete GPUs as well as in integrated/mobile ones? Or is that something that only happened after the switch to the unified shader model?
- kevingadd 3y ago
  It depends on the GPU, in some cases there is a direct pipeline from vertex shading to fragment shading. But typically (even on mobile GPUs) there is some sort of cache to exploit the fact that often the same vertex gets shaded multiple times. In tile-based rendering typically the shaded vertex data is all partitioned into "bins" that are used to do things like depth sorting, hidden surface removal etc. There's often a memory hierarchy as well - for example the "tile" memory might be special dedicated high-speed memory, as it was on the XBox 360. So you could end up with one type of memory being used for the input vertex/index data and a different kind used for the "bins" containing shaded vertex data. (Despite being a high-power desktop-grade GPU part, the XBox 360 had "predicated tiling" mode which would partition the screen up into big tiles, much like described in ARM's PDF. They did this to support multisampling at high resolutions.) Also, unless things have changed, modern NVIDIA GPUs are sort of tile based, albeit not in the same way as an ARM mobile GPU. See https://www.youtube.com/watch?v=Nc6R1hwXhL8 https://www.youtube.com/watch?v=Nc6R1hwXhL8 for a demo of this. This type of rasterization implies buffering the shaded vertex data in order to be able to rasterize multiple vertices in a single "tile" at once.
kosolam 3y ago
Awesome!
cududa 3y ago
Interestingly, this PDF causes iOS 17 beta Safari to crash
- saagarjha 3y ago
  This is what happens when mobile GPUs do not work
tedunangst 3y ago
There are more pages if you go to the original source. https://interactive.arm.com/story/the-arm-manga-guide-to-the-mali-gpu/page/1 https://interactive.arm.com/story/the-arm-manga-guide-to-the...
- TazeTSchnitzel 3y ago
  There are actually three volumes: https://developer.arm.com/en/dev2/Gaming%20Graphics%20and%20VR/FeaturedContent/Mali%20Manga/FeaturedContent-MaliManga-Header https://developer.arm.com/en/dev2/Gaming%20Graphics%20and%20... (Why are there several websites…)
dragontamer 3y ago
Did "Manga Guide" make a mobile GPU book? I can't say I'm personally too interested in mobile GPUs. I know they're a very different architecture than Desktop GPUs and have some important optimizations with regards to memory bandwidth. (Desktop GPUs can just run higher-power RAM for more bandwidth, IIRC Mobile GPUs need to rely upon optimizations that Desktop GPUs simply don't care about yet). EDIT: Oh wow, now that I'm done reading the .pdf, I think they did a good job explaining this in comic-book form. I can assume though that video game programmers who optimize for specifically mobile-GPUs can get a graphical advantage over their competitors though. So even if its not my cup of tea, its probably very useful to others. ---------- On the "Manga Guide" perspective: these books are a lot of fun and I feel like they're a good introduction. As a comic-book format, they are very quick to read. Its hit-and-miss though. "Manga Guide to Linear Algebra" is awful and uninspired. Skip, just not worth your time. But "Manga Guide to SQL" is great. I think the story about the Princess trying to organize Apples in her kingdom (and thinking about customers, businesses, etc. etc.) very naturally teaches SQL. So much of SQL and Databases are about learning a hypothetical business, that a grand story about a Fairy, a princess, a kingdom losing money that needs more organization (etc. etc.) really helps out. Knowing that Customer's Address and how it can conflict with other customers in 1st or 2nd normal form, but how 3rd normal form fixes the possible conflict (etc. etc.) solidifies SQL ideas and theories with a story. I think that's the key. Some subjects (and authors) are able to properly weave a story into the explanation. A subject like Linear Algebra probably can't have any story weaved in, so they kind of failed at that. SQL does, and I think a "Mobile GPU as a factory / tour of the factory comic book style" could make sense.
- hobs 3y ago
  Pretty much everyone I taught SQL I mapped the queries to natural questions anyone would have about a business that they were working at right then... because that's what it was basically invented for, is very good at it, and most people don't really care or need advanced features anyway.
- TT-392 3y ago
  This one isn't "manga guide" though. I don't think the source is even japanese, cause it reads from left to right (kinda jarring, reading a manga looking comic from left to right). I think this one just comes straight from arm.
gruez 3y ago
part 2: https://armkeil.blob.core.windows.net/developer/Files/pdf/graphics-and-multimedia/render-pass.pdf https://armkeil.blob.core.windows.net/developer/Files/pdf/gr...
leidenfrost 3y ago
Obligatory blog entry made by Alyssa when dissecting the M1 GPU hardware: https://rosenzweig.io/blog/asahi-gpu-part-1.html https://rosenzweig.io/blog/asahi-gpu-part-1.html
GaggiX 3y ago
That's not what I was expecting but I'm not complaining.
charcircuit 3y ago
Both desktop and mobile GPUs are tile based now. This is outdated.
- kevingadd 3y ago
  They're still a very different breed of "tile based", though.

172 points by goranmoomin 3y ago

I kind of got a reality check reading a Quora answer back in the day when I was hunting for GTA V on Android. There were a lot of scammy terrible apps (and still are).

amelius 3y ago

You can also ask your GPU how it works and to generate the explanation in manga style.

lxgr 3y ago

What's the "conveyor belt" between vertex and fragment shader? Doesn't communication between these two shaders happen via GPU memory in discrete GPUs as well as in integrated/mobile ones? Or is that something that only happened after the switch to the unified shader model?

kevingadd 3y ago
It depends on the GPU, in some cases there is a direct pipeline from vertex shading to fragment shading. But typically (even on mobile GPUs) there is some sort of cache to exploit the fact that often the same vertex gets shaded multiple times. In tile-based rendering typically the shaded vertex data is all partitioned into "bins" that are used to do things like depth sorting, hidden surface removal etc. There's often a memory hierarchy as well - for example the "tile" memory might be special dedicated high-speed memory, as it was on the XBox 360. So you could end up with one type of memory being used for the input vertex/index data and a different kind used for the "bins" containing shaded vertex data. (Despite being a high-power desktop-grade GPU part, the XBox 360 had "predicated tiling" mode which would partition the screen up into big tiles, much like described in ARM's PDF. They did this to support multisampling at high resolutions.) Also, unless things have changed, modern NVIDIA GPUs are sort of tile based, albeit not in the same way as an ARM mobile GPU. See https://www.youtube.com/watch?v=Nc6R1hwXhL8 https://www.youtube.com/watch?v=Nc6R1hwXhL8 for a demo of this. This type of rasterization implies buffering the shaded vertex data in order to be able to rasterize multiple vertices in a single "tile" at once.

kosolam 3y ago

Awesome!

cududa 3y ago

Interestingly, this PDF causes iOS 17 beta Safari to crash

saagarjha 3y ago
This is what happens when mobile GPUs do not work

tedunangst 3y ago

There are more pages if you go to the original source. https://interactive.arm.com/story/the-arm-manga-guide-to-the-mali-gpu/page/1 https://interactive.arm.com/story/the-arm-manga-guide-to-the...

TazeTSchnitzel 3y ago
There are actually three volumes: https://developer.arm.com/en/dev2/Gaming%20Graphics%20and%20VR/FeaturedContent/Mali%20Manga/FeaturedContent-MaliManga-Header https://developer.arm.com/en/dev2/Gaming%20Graphics%20and%20... (Why are there several websites…)

dragontamer 3y ago

Did "Manga Guide" make a mobile GPU book? I can't say I'm personally too interested in mobile GPUs. I know they're a very different architecture than Desktop GPUs and have some important optimizations with regards to memory bandwidth. (Desktop GPUs can just run higher-power RAM for more bandwidth, IIRC Mobile GPUs need to rely upon optimizations that Desktop GPUs simply don't care about yet). EDIT: Oh wow, now that I'm done reading the .pdf, I think they did a good job explaining this in comic-book form. I can assume though that video game programmers who optimize for specifically mobile-GPUs can get a graphical advantage over their competitors though. So even if its not my cup of tea, its probably very useful to others. ---------- On the "Manga Guide" perspective: these books are a lot of fun and I feel like they're a good introduction. As a comic-book format, they are very quick to read. Its hit-and-miss though. "Manga Guide to Linear Algebra" is awful and uninspired. Skip, just not worth your time. But "Manga Guide to SQL" is great. I think the story about the Princess trying to organize Apples in her kingdom (and thinking about customers, businesses, etc. etc.) very naturally teaches SQL. So much of SQL and Databases are about learning a hypothetical business, that a grand story about a Fairy, a princess, a kingdom losing money that needs more organization (etc. etc.) really helps out. Knowing that Customer's Address and how it can conflict with other customers in 1st or 2nd normal form, but how 3rd normal form fixes the possible conflict (etc. etc.) solidifies SQL ideas and theories with a story. I think that's the key. Some subjects (and authors) are able to properly weave a story into the explanation. A subject like Linear Algebra probably can't have any story weaved in, so they kind of failed at that. SQL does, and I think a "Mobile GPU as a factory / tour of the factory comic book style" could make sense.

hobs 3y ago
Pretty much everyone I taught SQL I mapped the queries to natural questions anyone would have about a business that they were working at right then... because that's what it was basically invented for, is very good at it, and most people don't really care or need advanced features anyway.
TT-392 3y ago
This one isn't "manga guide" though. I don't think the source is even japanese, cause it reads from left to right (kinda jarring, reading a manga looking comic from left to right). I think this one just comes straight from arm.

gruez 3y ago

part 2: https://armkeil.blob.core.windows.net/developer/Files/pdf/graphics-and-multimedia/render-pass.pdf https://armkeil.blob.core.windows.net/developer/Files/pdf/gr...

leidenfrost 3y ago

Obligatory blog entry made by Alyssa when dissecting the M1 GPU hardware: https://rosenzweig.io/blog/asahi-gpu-part-1.html https://rosenzweig.io/blog/asahi-gpu-part-1.html

GaggiX 3y ago

That's not what I was expecting but I'm not complaining.

charcircuit 3y ago

Both desktop and mobile GPUs are tile based now. This is outdated.

kevingadd 3y ago
They're still a very different breed of "tile based", though.