5 ms·

"Optimized for games" means "optimized for single-precision linear algebra", more or less.

tgb 10y ago
My experience is that double precision is very common on demanding game areas, notably physics. I recall older versions of the ODE physics engine recommending and defaulting to double precision and lots of newbies on the forums being surprised there wasn't much performance difference. That was all some time ago.
- yoklov 10y ago
  My experience is that it's extremely uncommon, including on physics systems. While I no longer work in games, I did for several years, I probably can count the times that I used double precision on one hand (if you exclude the JavaScript work that plagued the end of my game development career). The reason for this is simple -- it's twice as slow. The vector width is half the size, and so you can do half as many operations at a time.
  - tgb 10y ago
    My experience is just as an amateur, so it's only worth so much. I'm pretty sure though that the difference was much less than a factor of two.
    - loup-vaillant 10y ago
      Probably because double precision floats are just as fast as single precisions if you don't vectorise. I bet you didn't. This would also explain for instance why many programming languages drop single precision floats altogether: they don't plan to vectorize in the first place.
      - tgb 10y ago
        Yeah, it looks like ODE doesn't use SIMD or anything, and hence performs poorly compared to more modern engines: http://blog.wolfire.com/2010/03/Comparing-ODE-and-Bullet http://blog.wolfire.com/2010/03/Comparing-ODE-and-Bullet
- zubat 10y ago
  A pretty solid rule of thumb is that 32 bits has enough precision for rendering, physics needs doubles if it's going to use a lot of iterations. Simplified models like Super Mario jumps or the tractor beam in "Thrust" (single rigid joint) can get away with 16-bit fixed point precision. OTOH rendering of geometry only needs about as much precision as the display offers, which often means 8 bits on older hardware.
soviettoly 10y ago
This is what I came here to say. With comments in the article such as: "CPU designers see vastly more benefit to spending area on, e.g.,vectorized floating-point multipliers." followed by "Intel is doubling the vector size in its newest CPUs---again!---this time from 256 bits to 512 bits." Seems like they are being optimized to be better at vector math, and games just happen to highly use these pieces of HW.
- hutzlibu 10y ago
  > Seems like they are being optimized to be better at vector math, and games just happen to highly use these pieces of HW More likely the other way around ...
  - andrioni 10y ago
    Given that games tend to be deployed on a wide range of computers, it's hard for them to use newer x86 extensions (e.g. AVX), while most scientific computing applications tend to be compiled for a specific machine. To get to see the larger improvements, you must use the newer instructions and registers, like you can see in BLAS benchmarks[1]. [1]: https://www.bountysource.com/teams/openblas/fundraiser https://www.bountysource.com/teams/openblas/fundraiser
    - daemin 10y ago
      Yep, at my old job we still had to support Windows XP 32 bit for the game client (internal tools were Windows 7 64 bit) as so many people were still playing on systems. I don't remember if we could use SSE2 or what the minimum was in that regard.
    - alfalfasprout 10y ago
      Some compilers support multiple codepaths depending on the supported instruction set. Intel's C++ compiler makes this easy, for instance.
- j1vms 10y ago
  > Seems like they are being optimized to be better at vector math, and games just happen to highly use these pieces of HW. It may in fact be that desktop/mobile CPUs are being optimized for their contemporary benchmark suites, thus targeting the ensuing benefits in marketing. The benchmarks themselves were, for a fair amount of their existence, focused on games-related performance, at least from what I recall.
Florin_Andrei 10y ago
So then you better optimize your algorithms and apps for a world where CPUs are good at single-precision BLAS stuff.
pandaman 10y ago
Which is funny, because games would have benefited more from half (16 bit floats) HW support. There is almost no support on CPUs (X360's CPU had conversion to and from half, IIRC, and ARM in handhelds supposedly supports full half arithmetics), even less on x86/x64 CPUs specifically.
- yvdriess 10y ago
  The comedy here is that AMD and NVIDIA are adding it to CPU and GPU designs for the benefit of DNN training workloads; something that took off because of hardware designed for video games ;)

tgb 10y ago

My experience is that double precision is very common on demanding game areas, notably physics. I recall older versions of the ODE physics engine recommending and defaulting to double precision and lots of newbies on the forums being surprised there wasn't much performance difference. That was all some time ago.

yoklov 10y ago
My experience is that it's extremely uncommon, including on physics systems. While I no longer work in games, I did for several years, I probably can count the times that I used double precision on one hand (if you exclude the JavaScript work that plagued the end of my game development career). The reason for this is simple -- it's twice as slow. The vector width is half the size, and so you can do half as many operations at a time.
- tgb 10y ago
  My experience is just as an amateur, so it's only worth so much. I'm pretty sure though that the difference was much less than a factor of two.
  - loup-vaillant 10y ago
    Probably because double precision floats are just as fast as single precisions if you don't vectorise. I bet you didn't. This would also explain for instance why many programming languages drop single precision floats altogether: they don't plan to vectorize in the first place.
    - tgb 10y ago
      Yeah, it looks like ODE doesn't use SIMD or anything, and hence performs poorly compared to more modern engines: http://blog.wolfire.com/2010/03/Comparing-ODE-and-Bullet http://blog.wolfire.com/2010/03/Comparing-ODE-and-Bullet
zubat 10y ago
A pretty solid rule of thumb is that 32 bits has enough precision for rendering, physics needs doubles if it's going to use a lot of iterations. Simplified models like Super Mario jumps or the tractor beam in "Thrust" (single rigid joint) can get away with 16-bit fixed point precision. OTOH rendering of geometry only needs about as much precision as the display offers, which often means 8 bits on older hardware.

soviettoly 10y ago

This is what I came here to say. With comments in the article such as: "CPU designers see vastly more benefit to spending area on, e.g.,vectorized floating-point multipliers." followed by "Intel is doubling the vector size in its newest CPUs---again!---this time from 256 bits to 512 bits." Seems like they are being optimized to be better at vector math, and games just happen to highly use these pieces of HW.

hutzlibu 10y ago
> Seems like they are being optimized to be better at vector math, and games just happen to highly use these pieces of HW More likely the other way around ...
- andrioni 10y ago
  Given that games tend to be deployed on a wide range of computers, it's hard for them to use newer x86 extensions (e.g. AVX), while most scientific computing applications tend to be compiled for a specific machine. To get to see the larger improvements, you must use the newer instructions and registers, like you can see in BLAS benchmarks[1]. [1]: https://www.bountysource.com/teams/openblas/fundraiser https://www.bountysource.com/teams/openblas/fundraiser
  - daemin 10y ago
    Yep, at my old job we still had to support Windows XP 32 bit for the game client (internal tools were Windows 7 64 bit) as so many people were still playing on systems. I don't remember if we could use SSE2 or what the minimum was in that regard.
  - alfalfasprout 10y ago
    Some compilers support multiple codepaths depending on the supported instruction set. Intel's C++ compiler makes this easy, for instance.
j1vms 10y ago
> Seems like they are being optimized to be better at vector math, and games just happen to highly use these pieces of HW. It may in fact be that desktop/mobile CPUs are being optimized for their contemporary benchmark suites, thus targeting the ensuing benefits in marketing. The benchmarks themselves were, for a fair amount of their existence, focused on games-related performance, at least from what I recall.

Florin_Andrei 10y ago

So then you better optimize your algorithms and apps for a world where CPUs are good at single-precision BLAS stuff.

pandaman 10y ago

Which is funny, because games would have benefited more from half (16 bit floats) HW support. There is almost no support on CPUs (X360's CPU had conversion to and from half, IIRC, and ARM in handhelds supposedly supports full half arithmetics), even less on x86/x64 CPUs specifically.

yvdriess 10y ago
The comedy here is that AMD and NVIDIA are adding it to CPU and GPU designs for the benefit of DNN training workloads; something that took off because of hardware designed for video games ;)