Fortunately, it does make a difference. PIO is polling-base, whereas DMA is, lacking a better term (excuse my English), transaction-based. Since no CPU arbitration is needed, quite a few optimizations can be done because of this, like real, large block transfers. And if you happen to search the list archives, people have already reported significant gains when using these patches, so even if I'm talking bullocks empirical results do exist :)
Cheers, A. -- "I invented the term Object-Oriented, and I can tell you I did not have C++ in mind" -Alan Kay 2005/8/24, Jan Marten Simons <[EMAIL PROTECTED]>: > Víctor Córcoles López wrote: > > > Hello developers. My English is not good. > > > > I see that DMA in Hard Disks in guest OS Windows 2000/XP/2003 is not > > avalaible, it run in PIO mode. > > > > How can activate UDMA mode for hard disk ? > > > I don't think you'd get any advantage of activating DMA inside the qemu > guest-OS, as qemu has to proxy all rw-access into a file anyway, unless > you pass an actual device/partition to qemu. Besides qemu is emulating > the complete pci bus, which cannot use features of actual hardware in > the machine (e.g. your hdd or features your chipset provide). I guess it > would be possible to emulate uDMA inside the vm, too, but it's likely to > even slowdown the emulation. > > So long, > Jan _______________________________________________ Qemu-devel mailing list Qemu-devel@nongnu.org http://lists.nongnu.org/mailman/listinfo/qemu-devel