linux-kernel - Re: [PATCH RFC V3 2/4] kvm hypervisor : Add a hypercall to KVM hypervisor to support pv-ticketlocks

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Date:	Fri, 09 Dec 2011 16:29:06 +0530
From:	Raghavendra K T <raghukt@...ux.vnet.ibm.com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	Greg Kroah-Hartman <gregkh@...e.de>, KVM <kvm@...r.kernel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Sedat Dilek <sedat.dilek@...il.com>,
	Virtualization <virtualization@...ts.linux-foundation.org>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
	Dave Jiang <dave.jiang@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Gleb Natapov <gleb@...hat.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Ingo Molnar <mingo@...hat.com>, Rik van Riel <riel@...hat.com>,
	Xen <xen-devel@...ts.xensource.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Sasha Levin <levinsasha928@...il.com>,
	Suzuki Poulose <suzuki@...ux.vnet.ibm.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>
Subject: Re: [PATCH RFC V3 2/4] kvm hypervisor : Add a hypercall to KVM hypervisor
 to support pv-ticketlocks

On 12/08/2011 03:10 PM, Avi Kivity wrote:
> On 12/07/2011 06:46 PM, Raghavendra K T wrote:
>> On 12/07/2011 08:22 PM, Avi Kivity wrote:
>>> On 12/07/2011 03:39 PM, Marcelo Tosatti wrote:
>>>>> Also I think we can keep the kicked flag in vcpu->requests, no need
>>>>> for
>>>>> new storage.
>>>>
>>>> Was going to suggest it but it violates the currently organized
>>>> processing of entries at the beginning of vcpu_enter_guest.
>>>>
>>>> That is, this "kicked" flag is different enough from vcpu->requests
>>>> processing that a separate variable seems worthwhile (even more
>>>> different with convertion to MP_STATE at KVM_GET_MP_STATE).
>>>
>>> IMO, it's similar to KVM_REQ_EVENT (which can also cause mpstate to
>>> change due to apic re-evaluation).
>>>
>>
>> Ok, So what I understand is we have to either :
>> 1. retain current kick flag AS-IS but would have to make it migration
>> friendly. [I still have to get more familiar with migration side]
>> or
>> 2. introduce notion similar to KVM_REQ_PVLOCK_KICK(??) to be part of
>> vcpu->requests.
>>
>> So what would be better? Please let me know.
>>
>
> IMO, KVM_REQ.
>

Ok, 'll continue in this direction. Hmm I think now the race condition 
should be kept in mind, pointed by Marcello.

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