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

Avi Kivity
2011-02-17T09:58:42Z

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?

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error compiling committee.c: too many arguments to function