linux-kernel - Re: [PATCH RFC V3 2/3] kvm: Note down when cpu relax intercepted or pause loop exited

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Date:	Fri, 13 Jul 2012 09:05:59 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Christian Borntraeger <borntraeger@...ibm.com>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Ingo Molnar <mingo@...hat.com>, Avi Kivity <avi@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	S390 <linux-s390@...r.kernel.org>,
	Carsten Otte <cotte@...ibm.com>, KVM <kvm@...r.kernel.org>,
	chegu vinod <chegu_vinod@...com>,
	"Andrew M. Theurer" <habanero@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>, X86 <x86@...nel.org>,
	Gleb Natapov <gleb@...hat.com>, linux390@...ibm.com,
	Srivatsa Vaddagiri <srivatsa.vaddagiri@...il.com>,
	Joerg Roedel <joerg.roedel@....com>
Subject: Re: [PATCH RFC V3 2/3] kvm: Note down when cpu relax intercepted
 or pause loop exited

On 07/13/2012 01:32 AM, Christian Borntraeger wrote:
> On 12/07/12 21:18, Raghavendra K T wrote:
>> +#ifdef CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT
> [...]
>> +	struct {
>> +		bool cpu_relax_intercepted;
>> +		bool dy_eligible;
>> +	} ple;
>> +#endif
> [...]
>>   	}
>>   	vcpu->run = page_address(page);
>> +	vcpu->ple.cpu_relax_intercepted = false;
>> +	vcpu->ple.dy_eligible = false;
>
> This struct is only defined if CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT is set, but here it
> is always accessed. Will break on !x86&&  !s390.

Yes! I forgot about archs in init function.
How about having
#ifdef CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT
vcpu->ple.cpu_relax_intercepted = false;
vcpu->ple.dy_eligible = false;
#endif

This would solve all the problem.

>>
>>   	r = kvm_arch_vcpu_init(vcpu);
>>   	if (r<  0)
>> @@ -1577,6 +1579,7 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
>>   	int pass;
>>   	int i;
>>
>> +	me->ple.cpu_relax_intercepted = true;
>
> dito

currently vcpu_on_spin is used only by x86 and s390. so if some other
arch in future uses vcpu_on_spin, I believe they also have to enable
CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT
what do you think?

otherwise we have to add hook everywhere
>>   	/*
>>   	 * We boost the priority of a VCPU that is runnable but not
>>   	 * currently running, because it got preempted by something
>> @@ -1602,6 +1605,7 @@ void kvm_vcpu_on_spin(struct kvm_vcpu *me)
>>   			}
>>   		}
>>   	}
>> +	me->ple.cpu_relax_intercepted = false;
>
> again.
>
> maybe define static inline access functions in kvm_host.h that are no-ops
> if CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT is not set.
>

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