From mboxrd@z Thu Jan  1 00:00:00 1970
From: Gleb Natapov <gleb@redhat.com>
Subject: Re: [PATCH v4] KVM: nVMX: Fully support of nested VMX preemption
 timer
Date: Mon, 16 Sep 2013 12:09:11 +0300
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Cc: Arthur Chunqi Li <yzt356@gmail.com>, kvm@vger.kernel.org,
	jan.kiszka@web.de, yang.z.zhang@intel.com
To: Paolo Bonzini <pbonzini@redhat.com>
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On Mon, Sep 16, 2013 at 10:58:12AM +0200, Paolo Bonzini wrote:
> >>>  	vmx->__launched = vmx->loaded_vmcs->launched;
> >>> +	if (is_guest_mode(vcpu) && !(vmx->nested.nested_vmx_exit))
> >>> +		nested_adjust_preemption_timer(vcpu);
> >>
> >> Please leave the assignment to __launched last, since it's already
> >> initializing the asm below.
> >>
> >> I don't like the is_guest_mode check here... Maybe it's
> >> micro-optimizing, but I wonder if we already do too many checks in
> >> vmx_vcpu_run...  For example, is_guest_mode could be changed (I think)
> >> to a check for "vmx->loaded_vmcs == &vmx->vmcs1".
> >>
> > Why this will be more efficient that HF_GUEST_MASK check?
> 
> Because we have already loaded vmx->loaded_vmcs, so it's one memory
> access less.
> 
But we will have to load vmx->vmcs1 instead :) Looks like very minor
optimization if at all. If we could avoid additional if() at all
somehow, may be mimicking vcpu->requests in vmx to get rid of most ifs
there.

--
			Gleb.