From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [PATCH 2/3] KVM: VMX: Short circuit STI; HLT while an interrupt is pending Date: Wed, 16 Feb 2011 14:51:01 -0200 Message-ID: <20110216165101.GA15973@amt.cnet> References: <1297694537-9268-1-git-send-email-avi@redhat.com> <1297694537-9268-3-git-send-email-avi@redhat.com> <20110215203654.GA16010@amt.cnet> <4D5B927B.50903@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kvm@vger.kernel.org To: Avi Kivity Return-path: Received: from mx1.redhat.com ([209.132.183.28]:10150 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752627Ab1BPRT5 (ORCPT ); Wed, 16 Feb 2011 12:19:57 -0500 Received: from int-mx10.intmail.prod.int.phx2.redhat.com (int-mx10.intmail.prod.int.phx2.redhat.com [10.5.11.23]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id p1GHJvXP009036 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Wed, 16 Feb 2011 12:19:57 -0500 Content-Disposition: inline In-Reply-To: <4D5B927B.50903@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: 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 > >> --- > >> 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?