linux-kernel - Re: [patch -rt 2/2] KVM: lapic: mark LAPIC timer handler as irqsafe

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Date:	Fri, 5 Dec 2014 14:17:01 -0200
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	Luiz Capitulino <lcapitulino@...hat.com>,
	Steven Rostedt <srostedt@...hat.com>, kvm@...r.kernel.org
Subject: Re: [patch -rt 2/2] KVM: lapic: mark LAPIC timer handler as irqsafe

On Thu, Dec 04, 2014 at 02:53:26PM +0100, Paolo Bonzini wrote:
> 
> 
> On 25/11/2014 21:24, Thomas Gleixner wrote:
> > On Tue, 25 Nov 2014, Rik van Riel wrote:
> >> On 11/25/2014 12:21 PM, Marcelo Tosatti wrote:
> >>> Since lapic timer handler only wakes up a simple waitqueue,
> >>> it can be executed from hardirq context.
> >>>
> >>> Reduces average cyclictest latency by 3us.
> >>
> >> Can this patch be merged in the KVM tree, and go
> >> upstream via Paolo?
> > 
> > Not really as it has RT dependencies ....
> 
> Can hrtimer_start_expires even return ETIME on a non-RT kernel?  If yes,
> I can take patch 2.  If not, it's better to keep both patches in the RT
> tree.
> 
> Paolo

It can't. We're still evaluating the necessity of this patch, will
resubmit accordingly.

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