Re: [PATCH 2/3] KVM: VMX: Short circuit STI; HLT while an interrupt is pending

[Avi Kivity <avi@redhat.com>]

On 02/16/2011 06:51 PM, Marcelo Tosatti wrote:
> On Wed, Feb 16, 2011 at 11:01:47AM +0200, Avi Kivity wrote:
> >  On 02/15/2011 10:36 PM, Marcelo Tosatti wrote:
> >  >On Mon, Feb 14, 2011 at 04:42:16PM +0200, Avi Kivity wrote:
> >  >>   Short-circuit an STI; HLT sequence while an interrupt is pending:
> >  >>   instead of halting, re-entering the guest, and exiting immediately
> >  >>   on an interrupt window exit, go directly to the last step.
> >  >>
> >  >>   Saves a vmexit on workloads where interrupts are received synchronously;
> >  >>   an example is a disk backed by the host page cache where there is no
> >  >>   latency (from the guest's point of view) between the request and fulfilment.
> >  >>
> >  >>   Signed-off-by: Avi Kivity<avi@redhat.com>
> >  >>   ---
> >  >>    arch/x86/kvm/vmx.c |    9 +++++++++
> >  >>    1 files changed, 9 insertions(+), 0 deletions(-)
> >  >>
> >  >>   diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> >  >>   index ee1cd1a..541da0e 100644
> >  >>   --- a/arch/x86/kvm/vmx.c
> >  >>   +++ b/arch/x86/kvm/vmx.c
> >  >>   @@ -3437,6 +3437,15 @@ static int handle_interrupt_window(struct kvm_vcpu *vcpu)
> >  >>    static int handle_halt(struct kvm_vcpu *vcpu)
> >  >>    {
> >  >>    	skip_emulated_instruction(vcpu);
> >  >>   +	/*
> >  >>   +	 * Short-circuit an STI; HLT sequence while an interrupt is pending:
> >  >>   +	 * instead of halting, re-entering the guest, and exiting immediately
> >  >>   +	 * on an interrupt window exit, go directly to the last step.
> >  >>   +	 */
> >  >>   +	if ((to_vmx(vcpu)->cpu_based_vm_exec_control
> >  >>   +	&   CPU_BASED_VIRTUAL_INTR_PENDING)
> >  >>   +	&&   (kvm_get_rflags(vcpu)&   X86_EFLAGS_IF))
> >  >>   +		return handle_interrupt_window(vcpu);
> >  >>    	return kvm_emulate_halt(vcpu);
> >  >>    }
> >  >
> >  >Why does the normal vcpu entry path fails to inject the interrupt? Because after halt,
> >  >KVM_REQ_EVENT is not set?
> >
> >  Yes.  Also, we want to clear CPU_BASED_VIRTUAL_INTR_PENDING.
>
> Is there a reason why it cannot be handled in the main loop?

Don't follow.  What are you suggesting?

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