KVM: kvm_vm_ioctl_get_dirty_log restore "nothing dirty" optimization
authorRusty Russell <rusty@rustcorp.com.au>
Tue, 31 Jul 2007 09:57:47 +0000 (19:57 +1000)
committerAvi Kivity <avi@qumranet.com>
Sat, 13 Oct 2007 08:18:21 +0000 (10:18 +0200)
commit39214915f50f6ac2350355f2db63910d968fa790
tree0314e24ba07b5e0f20fa5ef71e82e2481a56b3f7
parentb114b0804df7131cb6764b948c1c530c834fa3c0
KVM: kvm_vm_ioctl_get_dirty_log restore "nothing dirty" optimization

kvm_vm_ioctl_get_dirty_log scans bitmap to see it it's all zero, but
doesn't use that information.

Avi says:
Looks like it was used to guard kvm_mmu_slot_remove_write_access();
optimizing the case where the guest just leaves the screen alone (which
it usually does, especially in benchmarks).

I'd rather reinstate that optimization.  See
90cb0529dd230548a7f0d6b315997be854caea1b where the damage was done.

It's pretty simple: if the bitmap is all zero, we don't need to do anything to
clean it.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Avi Kivity <avi@qumranet.com>
drivers/kvm/kvm_main.c