4 ms·

Through the electrical wires in the PCI express port.

danielmarkbruce 5y ago
I could be misunderstanding the context of the question, but I think OP is imagining some sophisticated communication logic involved at the chip level. The CPU doesn't know anything much about the GPU other than it's there and data can be sent back and forth to it. It doesn't know what any of the data means. I think the logic OP imagines does exist, but it's actually in the compiler (eg the cuda compiler), figuring exactly what bytes to send which will start a program etc.
- coolspot 5y ago
  Not in the compiler but in GPU driver. A graphic program (or compute) just calls APIs (DirectX/Vulkan/CUDA) of a driver, which then knows how to do that on a low-level writing to particular regions of RAM mapped to GPU registers.
  - danielmarkbruce 5y ago
    Yes! This is correct. My bad, it's been too long. I guess either way the point is that it's done in software, not hardware.
    - lxgr 5y ago
      There's also odd/interesting architectures like one of the earlier Raspberry Pis, where the GPU was actually running its own operating system that would take care of things like shader compilation. In that case, what's actually being written to shared/mapped memory is very high level instructions that are then compiled or interpreted on the GPU (which is really an entire computer, CPU and all) itself.
alberth 5y ago
Nit pick… Technically it’s not “through” the electrical wires, it’s actually through the electrical field created around the electrical wires. Veritasium explains https://youtu.be/bHIhgxav9LY https://youtu.be/bHIhgxav9LY
- tux3 5y ago
  Nitpicking the nitpick: the energy is what's in the fields, but the electrical wires aren't just for show, the electrons do need to be able to move in the wire for there to be a current, and the physical properties of the wire have a big impact on the signal. So things get very complicated and unintuitive, especially at high frequencies, but it's okay to say through the wire!
  - a9h74j 5y ago
    And as you might be alluding, particularly high frequencies: in the skin (via skin effect) of the wire! I'll confess I have never seen a plot of actual rms current density vs radius related to skin effect.

I could be misunderstanding the context of the question, but I think OP is imagining some sophisticated communication logic involved at the chip level. The CPU doesn't know anything much about the GPU other than it's there and data can be sent back and forth to it. It doesn't know what any of the data means. I think the logic OP imagines does exist, but it's actually in the compiler (eg the cuda compiler), figuring exactly what bytes to send which will start a program etc.

coolspot 5y ago
Not in the compiler but in GPU driver. A graphic program (or compute) just calls APIs (DirectX/Vulkan/CUDA) of a driver, which then knows how to do that on a low-level writing to particular regions of RAM mapped to GPU registers.
- danielmarkbruce 5y ago
  Yes! This is correct. My bad, it's been too long. I guess either way the point is that it's done in software, not hardware.
  - lxgr 5y ago
    There's also odd/interesting architectures like one of the earlier Raspberry Pis, where the GPU was actually running its own operating system that would take care of things like shader compilation. In that case, what's actually being written to shared/mapped memory is very high level instructions that are then compiled or interpreted on the GPU (which is really an entire computer, CPU and all) itself.

alberth 5y ago

Nit pick… Technically it’s not “through” the electrical wires, it’s actually through the electrical field created around the electrical wires. Veritasium explains https://youtu.be/bHIhgxav9LY https://youtu.be/bHIhgxav9LY

tux3 5y ago
Nitpicking the nitpick: the energy is what's in the fields, but the electrical wires aren't just for show, the electrons do need to be able to move in the wire for there to be a current, and the physical properties of the wire have a big impact on the signal. So things get very complicated and unintuitive, especially at high frequencies, but it's okay to say through the wire!
- a9h74j 5y ago
  And as you might be alluding, particularly high frequencies: in the skin (via skin effect) of the wire! I'll confess I have never seen a plot of actual rms current density vs radius related to skin effect.