On Mon, May 11, 2015 at 01:47:57PM +0100, Paul Durrant wrote: > Currently running make defconfig will leave the above turned off which, > at least for the Xen/QEMU use-case, means VMs will boot very slowly. > There seems to have been some concern over non-QEMU use of ATA_DMA about > five years ago, but I can find no particular concern over ATA_PIO32. > Given the increased use of QEMU and Xen in that period it would seem > like a good idea to default both of these on now. This patch does that.
The DMA support is known to be not correct for real hardware - correct code would negotiate the DMA rate with the drive (and also do things like detecting a 66Mhz PATA cable). The code is only really useful on emulators and when one knows that the drive is really a SATA drive connected to a controller that is doing PATA emulation. The 32bit PIO mode has a minimal speed improvement and it is known to not work on some real hardware controllers. If one is concerned about VM boot speed, why not just use AHCI or virtio? -Kevin _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
