On Wed, May 5, 2010 at 5:20 PM, Frank Berreth <frankber@xxxxxxxxxx> wrote: > Hi there, > this is just an update if you are interested in the outcome. I turns out > that my initial assumption that there would be page faults/trapping on the > memory pages was false. The reason the throughput is so low is because the > memory was mapped non-cached. The VGA driver and the ivshmem driver use > pci_ioremap_bar which will *always* map the PCI bar non-cached (even the > resourceX_wc). > Changing the driver(s) to use ioremap_cache or ioremap_wc speeds up things > quite a bit. I don't know if VGA framebuffer was always mapped this way -- > it appears on a real system that usually graphics memory is mapped WC. > Mapping it UC would cause quite a performance degradation. This could be the > reason for the reported VGA performance drop in another email thread. IMHO, > since QEMU emulates VGA, this could be mapped WB. > Thanks, > Frank. > Hi Frank, Thanks for the note. I'll make the change to cached and see if that helps with some of the tests I'm running. Cheers, Cam -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
