Re: [patch 2/2] KVM: PIT: provide an option to disable interrupt reinjection

[Avi Kivity <avi@redhat.com>]

Marcelo Tosatti wrote:
> Certain clocks (such as TSC) in older 2.6 guests overaccount for lost
> ticks, causing severe time drift. Interrupt reinjection magnifies the
> problem.
>
> Provide an option to disable it.
>
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
>
> Index: kvm/arch/x86/kvm/i8254.c
> ===================================================================
> --- kvm.orig/arch/x86/kvm/i8254.c
> +++ kvm/arch/x86/kvm/i8254.c
> @@ -201,6 +201,9 @@ static int __pit_timer_fn(struct kvm_kpi
>  	if (!atomic_inc_and_test(&pt->pending))
>  		set_bit(KVM_REQ_PENDING_TIMER, &vcpu0->requests);
>  
> +	if (pt->no_reinject)
> +		atomic_set(&pt->pending, 1);
> +
>   

What about moving this to the place where we atomic_inc()?  Any reason 
not to?

> --- kvm.orig/arch/x86/kvm/i8254.h
> +++ kvm/arch/x86/kvm/i8254.h
> @@ -9,6 +9,7 @@ struct kvm_kpit_timer {
>  	s64 period; /* unit: ns */
>  	s64 scheduled;
>  	atomic_t pending;
> +	bool no_reinject;
>  };
>   

Negative logic = !good.  Call it reinject and init to true.

> @@ -991,6 +991,7 @@ int kvm_dev_ioctl_check_extension(long e
>  	case KVM_CAP_NOP_IO_DELAY:
>  	case KVM_CAP_MP_STATE:
>  	case KVM_CAP_SYNC_MMU:
> +	case KVM_CAP_PIT_NO_REINJECT:
>   

Negative logic. PIT_REINJECT_CONTROL?

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