Re: [PATCH] kvm_vm_ioctl_get_dirty_log restore "nothing dirty" optimization

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Rusty Russell wrote:
> 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
> 	66d8a4e4d4bd470216028daabb9d887b73259c96 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-8n+1lVoiYb80n/F98K4Iww@public.gmane.org>
>
> diff -r 66566cf6b576 drivers/kvm/kvm_main.c
> --- a/drivers/kvm/kvm_main.c	Fri Jul 27 16:27:11 2007 +1000
> +++ b/drivers/kvm/kvm_main.c	Mon Jul 30 23:15:47 2007 +1000
> @@ -838,11 +838,13 @@ static int kvm_vm_ioctl_get_dirty_log(st
>  	if (copy_to_user(log->dirty_bitmap, memslot->dirty_bitmap, n))
>  		goto out;
>  
> -	spin_lock(&kvm->lock);
> -	kvm_mmu_slot_remove_write_access(kvm, log->slot);
> -	kvm_flush_remote_tlbs(kvm);
> -	memset(memslot->dirty_bitmap, 0, n);
> -	spin_unlock(&kvm->lock);
> +	if (any) {
> +		spin_lock(&kvm->lock);
> +		kvm_mmu_slot_remove_write_access(kvm, log->slot);
> +		kvm_flush_remote_tlbs(kvm);
> +		memset(memslot->dirty_bitmap, 0, n);
> +		spin_unlock(&kvm->lock);
> +	}
>  

spin_lock()?  my, that's so last week.  kvm->lock is a mutex.


-- 
error compiling committee.c: too many arguments to function


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