> > I hope, hope, hope that nobody is really setting up firmware to > respond to PCIe reads of the framebuffer. I don't see how this could > be.
to read directly from the framebuffer, the video memory in the card would have to be directly attached to the pcie interface on the card. i believe that would require a general memory bus & coherency protcol arbitrating between memory, pcie, and the gpu. (the old-fashioned solution to this was dual-ported ram.) of course, this is speculation. but i think that it's safely not as simple as just reading video memory. also, even with the mtrr the reads are not read combining. it's uncachable for reads, so it's 32bit pio. > > > > as one data point, my pcie-based nvidia card raises windows much > > more slowly than the older agp one that i have. and the pcie card > > has every advantage. the agp card runs in a intel celery system. > > What OS? are you sure this is not an os setup issue? uh, plan 9. - erik p.s. i found this link from nvidia on how to make textures faster. one thing they're concerned about is the *latency* of downloading textures. that might apply to reading the fb as well. http://download.nvidia.com/developer/Papers/2005/Fast_Texture_Transfers/Fast_Texture_Transfers.pdf
