linux-kernel - Re: [RFC][PATCH] Improving directed yield scalability for PLE handler

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Date:	Mon, 10 Sep 2012 16:31:48 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	habanero@...ux.vnet.ibm.com,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>,
	Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Ingo Molnar <mingo@...hat.com>, KVM <kvm@...r.kernel.org>,
	chegu vinod <chegu_vinod@...com>,
	LKML <linux-kernel@...r.kernel.org>, X86 <x86@...nel.org>,
	Gleb Natapov <gleb@...hat.com>,
	Srivatsa Vaddagiri <srivatsa.vaddagiri@...il.com>
Subject: Re: [RFC][PATCH] Improving directed yield scalability for PLE handler

On 09/10/2012 04:19 PM, Peter Zijlstra wrote:
> On Mon, 2012-09-10 at 15:12 -0500, Andrew Theurer wrote:
>> +       /*
>> +        * if the target task is not running, then only yield if the
>> +        * current task is in guest mode
>> +        */
>> +       if (!(p_rq->curr->flags & PF_VCPU))
>> +               goto out_irq;
>
> This would make yield_to() only ever work on KVM, not that I mind this
> too much, its a horrid thing and making it less useful for (ab)use is a
> good thing, still this probably wants mention somewhere :-)

Also, it would not preempt a non-kvm task, even if we need
to do that to boost a VCPU. I think the lines above should
be dropped.

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