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

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Message-ID: <4EDF94F0.2080201@linux.vnet.ibm.com>
Date:	Wed, 07 Dec 2011 22:01:44 +0530
From:	Raghavendra K T <raghukt@...ux.vnet.ibm.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
CC:	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>, Avi Kivity <avi@...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 12/07/2011 06:03 PM, Marcelo Tosatti wrote:
> On Wed, Dec 07, 2011 at 05:24:59PM +0530, Raghavendra K T wrote:
>> On 12/07/2011 04:18 PM, Marcelo Tosatti wrote:
>> Yes you are right. It was potentially racy and it was harmful too!.
>> I had observed that it was stalling the CPU before I introduced
>> kicked flag.
>>
>> But now,
>>
>> vcpu->kicked = 1  ==>  kvm_make_request(KVM_REQ_UNHALT, vcpu); ==>
>
> Ok, please use a more descriptive name, such as "pvlock_kicked" or
> something.
>

Yes, pvlock_kicked seems good. 'll use same unless something else
flashes.

>>
>> __vcpu_run() ==>  kvm_check_request(KVM_REQ_UNHALT, vcpu) ==>
>>
>> vcpuN->mp_state = KVM_MP_STATE_RUNNABLE; so eventually we will end up
>> in RUNNABLE.
>>
>> Also Avi pointed that, logically kvm_arch_vcpu_ioctl_set_mpstate should
>> be called only in vcpu thread, so after further debugging, I noticed
>> that,  setting vcpuN->mp_state = KVM_MP_STATE_RUNNABLE; is not
>> necessary.
>> I 'll remove that in the next patch. Thanks for pointing.
>
> In fact you don't need kvm_arch_vcpu_ioctl_set_mpstate either, only the
> new "kicked" flag.
>

True indeed, I meant the same.

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