alt Hacker NewsMost CPUs can address 48 bits of physical memory (hundreds of terabytes), why is that even a problem ? Is it just some hardware limitation somewhere else or badly written firmware ?
Replies
dougcalobrisi • today at 5:11 PM
Yeah, it's the firmware. It's an AM4 board, and the BIOS only gives PCI devices the space from the top of RAM up to 512 GB. Each 32 GB BAR has to start on a 32 GB boundary, and its small doorbell BAR spills into the next slot, so each card needs 64 GB. Six won't fit. So I turn Resizable BAR off in the BIOS and resize the four R9700s from Linux, where I hit the kernel bug.
➕ show 3 replies
There was never a concerted effort in the PC ecosystem to force all peripherals and firmware to drop 32-bit compatibility. At some point after a decade or two of x86-64 CPUs, we should have started making GPUs that simply exposed all of their VRAM to be mapped by the host by default, instead of retaining compatibility hacks like only mapping 256MB by default. Resizable BARs should have happened at least a decade earlier, and should have been phased out by now in favor of just always mapping all the VRAM.