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

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Message-ID: <5003C4E5.8000606@linux.vnet.ibm.com>
Date:	Mon, 16 Jul 2012 13:08:13 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
CC:	Christian Borntraeger <borntraeger@...ibm.com>,
	"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 07:24 PM, Srikar Dronamraju 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.
>
> How about moving this struct definition outside the CONFIG.
> i.e it would be available by default.
> If any arch cares to use vcpu_on_spin(), they would get the benefit by
> default.
>
> This would avoid all the CONFIG magic that we would have to do
> otherwise.
>

Okay, after discussing with Christian,
- even if ppc uses vcpu_on spin we will still be left with ia64 (though
broken currently) and arm (is on way).
- those who want to opt-out of this optimization but still wish to use
vcpu_spin, we have flexibility.

So with that in mind I am spinning V4 with
CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT. Let us see how it goes.

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