Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=39214915f50f6ac2350355f2db63910d968fa790
Commit: 39214915f50f6ac2350355f2db63910d968fa790
Parent: b114b0804df7131cb6764b948c1c530c834fa3c0
Author: Rusty Russell <[EMAIL PROTECTED]>
AuthorDate: Tue Jul 31 19:57:47 2007 +1000
Committer: Avi Kivity <[EMAIL PROTECTED]>
CommitDate: Sat Oct 13 10:18:21 2007 +0200
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 <[EMAIL PROTECTED]>
Signed-off-by: Avi Kivity <[EMAIL PROTECTED]>
---
drivers/kvm/kvm_main.c | 13 ++++++++-----
1 files changed, 8 insertions(+), 5 deletions(-)
diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index bfb1b6d..5dee302 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -803,11 +803,14 @@ static int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
if (copy_to_user(log->dirty_bitmap, memslot->dirty_bitmap, n))
goto out;
- mutex_lock(&kvm->lock);
- kvm_mmu_slot_remove_write_access(kvm, log->slot);
- kvm_flush_remote_tlbs(kvm);
- memset(memslot->dirty_bitmap, 0, n);
- mutex_unlock(&kvm->lock);
+ /* If nothing is dirty, don't bother messing with page tables. */
+ if (any) {
+ mutex_lock(&kvm->lock);
+ kvm_mmu_slot_remove_write_access(kvm, log->slot);
+ kvm_flush_remote_tlbs(kvm);
+ memset(memslot->dirty_bitmap, 0, n);
+ mutex_unlock(&kvm->lock);
+ }
r = 0;
-
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