Question Does enabling Resizable Bar increase or decrease PCIe traffic ?

[80251]

From what I understand, Resizable Bar just increases the aperture size to access the GPU's VRAM.
I'm guessing this would increase PCIe traffic because you can transfer more data at a time without changing the aperture window. Does anyone know to what extent a larger resizable bar or SAM affects PCIe traffic?

 

[beyondlogic]

From what I understand, Resizable Bar just increases the aperture size to access the GPU's VRAM.
I'm guessing this would increase PCIe traffic because you can transfer more data at a time without changing the aperture window. Does anyone know to what extent a larger resizable bar or SAM affects PCIe traffic?

Instead of small chunks of information being sent from CPU to GPU it instead sends all of the information the GPU requests as one big package instead of say it going to ram instead it makes a direct path between CPU and GPU

 

[kerberos_20]

it also needs messaged signal interrupts enabled, so it does improve latency just from msi alone, since cpu can flush all data with single i/o, cpus interrupts needed are lover, thus it should improve traffic as traffic happens concurently rather than waiting in queue

 

[80251]

@kerberos_20
So the net effect would be more traffic over the PCIe bus? Is SAM/resizable BAR a tech that direct storage could leverage? Or does direct storage replace it?

 

[80251]

Instead of small chunks of information being sent from CPU to GPU it instead sends all of the information the GPU requests as one big package instead of say it going to ram instead it makes a direct path between CPU and GPU

So it streams the data off secondary storage? If the PCIe bus is connected directly to the CPU wouldn't data always be going via a direct path between CPU and GPU?

 

[kerberos_20]

@kerberos_20
So the net effect would be more traffic over the PCIe bus? Is SAM/resizable BAR a tech that direct storage could leverage? Or does direct storage replace it?

that has nothing to do with direct storage
this image is from when direct storage is not used:

https://imgur.com/fHav3rP

View: https://imgur.com/fHav3rP

SAM/ReBAR will just affect GPU copy part


direct storage just changes it so that CPU sends compressed data directly to GPU (which is small assets/textures) where gpu decompresses it

 

[beyondlogic]

So it streams the data off secondary storage? If the PCIe bus is connected directly to the CPU wouldn't data always be going via a direct path between CPU and GPU?

Not exactly so when a pc does something

The CPU normally has to send everything in chunks threw ram think of this a game of pass the parcel.

Cpu- ram then ram sends that data to both hd and GPU depending on what data is needed then cpu access ram to get that info that's been sent back by the GPU.

Now resize bar essentially gives the CPU and GPU direct access to each other so the CPU can directly talk to GPUs memory pool thus not having to wait for the system ram to send it.

 

[80251]

Not exactly so when a pc does something

The CPU normally has to send everything in chunks threw ram think of this a game of pass the parcel.

Cpu- ram then ram sends that data to both hd and GPU depending on what data is needed then cpu access ram to get that info that's been sent back by the GPU.

Now resize bar essentially gives the CPU and GPU direct access to each other so the CPU can directly talk to GPUs memory pool thus not having to wait for the system ram to send it.

' The CPU normally has to send everything in chunks threw ram...' But doesn't all the data have to go through the CPU from RAM to even get to the GPU? In the old days you could stream data across a northbridge to a videocard (similarly to DMA), but now it all has to go through the CPU, it's the only device that has a physical connection to the GPU or the RAM for that matter.