On 10.02.2010 15:12, Pauli Nieminen wrote: > Hi! > > I made some testing how fast my system can move data to VRAM/GTT and I > got very interestig results: > > (II) RADEON(0): BENCH: copy 3129344 bytes to vram took 78595us, > resulting in 39Mbps "Mbps" is a bit confusing I can only read that as Megabit per second which is even more pathetic :-)
> (II) RADEON(0): BENCH: copy 3129344 bytes to gtt took 11411us, > resulting in 274Mbps > (II) RADEON(0): BENCH: copy 3129344 bytes to gtt took 8431us, > resulting in 371Mbps > (II) RADEON(0): BENCH: copy 3129344 bytes to vram took 75773us, > resulting in 41Mbps > (II) RADEON(0): BENCH: copy 3129344 gtt to vram took 3143us, resulting > in 995Mbps > > > So direct write to VRAM operates only at 40 mega bytes per second. > That is insanely slow. I hope we won't hit that kind of limit anywhere > in any code. > > I did check that VRAM is WC cached in /proc/mtrr. But still it is > surprising slow. Isn't that something which fast writes should help with, an option we never really got to work? I agree though it's really bad. In any case I think it would be interesting to repeat those tests on pci/pcie cards. > > But most insane result is that CPU can only write to GTT max 371 Mbps > while GPU can do gtt to vram at 995Mbps. More insane in that results > is that I was nearly sure that my memory can't operate that fast but > still when code to check vram content runs everything is correctly in > vram! What did GPU/AGP did to cheat that much? Is there some error in > my test case? > > System is: > Athlon mobility XP at 2.1Ghz > 333MHz ddr memory > AGP 8x bus to mobility radeon 9200. Why is that surprsing? AGP 8x is good for ~2GB/s. Your memory is good for ~2.7GB/s. Granted, those are theoretical peak values, but getting 1GB/s out of it looks very reasonable. Looks to me like CPU->GTT is slow rather than GTT->VRAM insanely fast... Roland _______________________________________________ xorg-driver-ati mailing list [email protected] http://lists.x.org/mailman/listinfo/xorg-driver-ati
