linux-kernel - Re: [RFC] KVM: optimize the kvm_vcpu_on

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Date:   Mon, 31 Jul 2017 19:32:26 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Christoffer Dall <cdall@...aro.org>,
        "Longpeng(Mike)" <longpeng2@...wei.com>
Cc:     pbonzini@...hat.com, rkrcmar@...hat.com, agraf@...e.com,
        borntraeger@...ibm.com, cohuck@...hat.com,
        christoffer.dall@...aro.org, marc.zyngier@....com,
        james.hogan@...tec.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, weidong.huang@...wei.com,
        arei.gonglei@...wei.com, wangxinxin.wang@...wei.com,
        longpeng.mike@...il.com
Subject: Re: [RFC] KVM: optimize the kvm_vcpu_on_spin

On 31.07.2017 15:22, Christoffer Dall wrote:
> On Sat, Jul 29, 2017 at 02:22:57PM +0800, Longpeng(Mike) wrote:
>> We had disscuss the idea here:
>> https://www.spinics.net/lists/kvm/msg140593.html
> 
> This is not a very nice way to start a commit description.
> 
> Please provide the necessary background to understand your change
> directly in the commit message.
> 
>>
>> I think it's also suitable for other architectures.
>>
> 
> I think this sentence can go in the end of the commit message together
> with your explanation of only doing this for x86.
> 
> By the way, the ARM solution should be pretty simple:
> 
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index a39a1e1..b9f68e4 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -416,6 +416,11 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *v)
>  		&& !v->arch.power_off && !v->arch.pause);
>  }
>  
> +bool kvm_arch_vcpu_in_kernel(struct kvm_vcpu *vcpu)
> +{
> +	return vcpu_mode_priv(vcpu);
> +}
> +
>  /* Just ensure a guest exit from a particular CPU */
>  static void exit_vm_noop(void *info)
>  {
> 
> 


This one should work for s390x, no caching (or special access patterns
like on x86) needed:

+++ b/arch/s390/kvm/kvm-s390.c
@@ -2447,6 +2447,11 @@ int kvm_arch_vcpu_runnable(struct kvm_vcpu *vcpu)
        return kvm_s390_vcpu_has_irq(vcpu, 0);
 }

+bool kvm_arch_vcpu_in_kernel(struct kvm_vcpu *vcpu)
+{
+       return !(vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE);
+}
+
 void kvm_s390_vcpu_block(struct kvm_vcpu *vcpu)
 {
        atomic_or(PROG_BLOCK_SIE, &vcpu->arch.sie_block->prog20);



-- 

Thanks,

David