Re: [patch 3/4] KVM: use smp_send_reschedule in kvm_vcpu_kick

[Gleb Natapov <gleb@redhat.com>]

On Thu, May 07, 2009 at 05:55:12PM -0300, mtosatti@redhat.com wrote:
> KVM uses a function call IPI to cause the exit of a guest running on a
> physical cpu. For virtual interrupt notification there is no need to
> wait on IPI receival, or to execute any function.
> 
> This is exactly what the reschedule IPI does, without the overhead
> of function IPI. So use it instead of smp_call_function_single in
> kvm_vcpu_kick.
> 
> Also change the "guest_mode" variable to a bit in vcpu->requests, and
> use that to collapse multiple IPI's that would be issued between the
> first one and zeroing of guest mode.
> 
> This allows kvm_vcpu_kick to called with interrupts disabled.
> 
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> 
Acked-by: Gleb Natapov <gleb@redhat.com>

Except one small nitpick below.
> Index: kvm-pending/arch/x86/kvm/x86.c
> ===================================================================
> --- kvm-pending.orig/arch/x86/kvm/x86.c
> +++ kvm-pending/arch/x86/kvm/x86.c
> @@ -3259,6 +3259,9 @@ static int vcpu_enter_guest(struct kvm_v
>  
>  	local_irq_disable();
>  
> +	clear_bit(KVM_REQ_KICK, &vcpu->requests);
> +	smp_mb__after_clear_bit();
> +
>  	if (vcpu->requests || need_resched() || signal_pending(current)) {
>  		local_irq_enable();
>  		preempt_enable();
> @@ -3266,13 +3269,6 @@ static int vcpu_enter_guest(struct kvm_v
>  		goto out;
>  	}
>  
> -	vcpu->guest_mode = 1;
> -	/*
> -	 * Make sure that guest_mode assignment won't happen after
> -	 * testing the pending IRQ vector bitmap.
> -	 */
> -	smp_wmb();
> -
Can you leave this comment. I like it :)

--
			Gleb.