linux-kernel - Re: [PATCH RFC V5 2/6] kvm hypervisor : Add a hypercall to KVM hypervisor to support pv-ticketlocks

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Message-ID: <4F8D168B.7090806@linux.vnet.ibm.com>
Date:	Tue, 17 Apr 2012 12:36:51 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	X86 <x86@...nel.org>, Avi Kivity <avi@...hat.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Alexander Graf <agraf@...e.de>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Gleb Natapov <gleb@...hat.com>,
	Randy Dunlap <rdunlap@...otime.net>, linux-doc@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>,
	Virtualization <virtualization@...ts.linux-foundation.org>,
	Xen <xen-devel@...ts.xensource.com>,
	Sasha Levin <levinsasha928@...il.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
Subject: Re: [PATCH RFC V5 2/6] kvm hypervisor : Add a hypercall to KVM hypervisor
 to support pv-ticketlocks

On 04/12/2012 05:59 AM, Marcelo Tosatti wrote:
> On Wed, Apr 11, 2012 at 09:06:29PM -0300, Marcelo Tosatti wrote:
>> On Fri, Mar 23, 2012 at 01:37:04PM +0530, Raghavendra K T wrote:
>>> From: Srivatsa Vaddagiri<vatsa@...ux.vnet.ibm.com>
>>>
[...]

		barrier();
>>
>> Is it always OK to erase the notification, even in case an unrelated
>> event such as interrupt was the source of wakeup?
>
> Note i am only asking whether it is OK to lose a notification, not
> requesting a change to atomic test-and-clear.

Yes.. got your point.
IMO, this is the only (safe) place where it can clear
kicked(pv_unhalted) flag. Since it is going to be runnable.

and you are also right in having concern on unwanted clear of flag
since that would result in vcpu /vm hangs eventually.

Hope I did not miss anything.

>
> It would be nice to have a comment explaining it.
>

Sure will do that

>>

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