On Wed, Mar 30, 2011 at 12:38:53PM +0200, Avi Kivity wrote: > On 03/29/2011 02:08 PM, Gleb Natapov wrote: > >Currently we sync registers back and forth before/after exiting > >to userspace for IO, but during IO device model shouldn't need to > >read/write the registers, so we can as well skip those sync points. The > >only exaception is broken vmware backdor interface. The new code sync > >registers content during IO only if registers are read from/written to > >by userspace in the middle of the IO operation and this almost never > >happens in practise. > > While this is a nice idea, how much does it save in practice? It > does introduce more complexity. > I haven't measured, but can try to do so. It eliminates two copies of all registers on each MMIO/PIO read. I expect this to be measurable in workloads that do many such reads. -- Gleb. -- 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
