Host CPU accesses: HOST_COHERENT explanation #1
Description
Hello!
First of all, thank you very much for the time you invested in this article!
I'm trying to understand concept of system memory visible to GPU and write-combined memory. I read papers regarding the topic and still can't get full image in my mind.
What you wrote there:
"Writes are cached a little bit - bytes written to the same cache line are collected in a write buffer, and eventually the write buffer will be flushed to VRAM in a single memory transaction."
What concerns me:
write combined memory is system memory(located in RAM, not VRAM) as far as I got it right. Then, assume CPU writes to region of write-combined memory(RAM) and then GPU will access that memory through PCIe and put it in it's caches eventually. This doesn't look like CPU will write anything to VRAM in here.
I might got something wrong or just didn't understand the concept of write-combined memory correct.
If you can explain this a bit, it would be very great.