linux-kernel - Re: [PART1 RFC 5/9] svm: Add VMEXIT handlers for AVIC

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Date:	Thu, 3 Mar 2016 11:50:24 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
	Radim Krčmář <rkrcmar@...hat.com>
Cc:	joro@...tes.org, alex.williamson@...hat.com, gleb@...nel.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, wei@...hat.com,
	sherry.hurwitz@....com, "Wu, Feng" <feng.wu@...el.com>
Subject: Re: [PART1 RFC 5/9] svm: Add VMEXIT handlers for AVIC



On 03/03/2016 11:42, Suravee Suthikulpanit wrote:
> In facts, instead of setting up the vAPIC backing page address when
> calling kvm_arch_vcpu_load(), we should be able to do it when calling
> kvm_arch_vcpu_sched_in(). This seems more appropriate since the
> kvm_arch_vcpu_load() is also called in many unnecessary occasions via
> vcpu_load() (in the arch/x86/kvm/x86.c). The same goes for the
> kvm_arch_vcpu_put().
> 
> However, there is no kvm_arch_vcpu_sched_out(). But that can be added
> easily.
> 
> What do you think?

How much code is involved?  It seems an unnecessary complication...
Unless you can profile a difference, I would leave it in
kvm_arch_vcpu_load()/kvm_arch_vcpu_put().

Note that sched_in and sched_out are not called once per invocation of
KVM_RUN---only through the preempt notifiers.  So I'm not sure it is
enough to use sched_in and sched_out.

Paolo