On Thu, Apr 09, 2015 at 05:53:59PM +0100, Marc Zyngier wrote: > The world switch spends quite some time dealing with the FP/SIMD > registers, as the state is quite sizeable (32 128bit registers, > plus some crumbs on the side). We save/restore them on each > entry/exit, so that both the host and the guest always see > the state they expect. > > But let's face it: the host kernel doesn't care. It is the host > userspace that actually cares about FP. An obvious improvement is > to remove the save/restore from the world switch, and only perform > it when we're about to enter/exit the guest (by plugging it into > vcpu_load/vcpu_put). The effect is pretty spectacular when running > hackbench (which is the only benchmark worth looking at): > so the kernel never uses fp/simd registers for stuff like memcopies etc.? Can we also make a similar change for ARM on the 32-bit side? -Christoffer -- 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
