Date: Tue, 17 Nov 2015 04:57:21 -0800
From: Jacob Pan <jacob.jun.pan@linux.intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Josh Triplett <josh@joshtriplett.org>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        John Stultz <john.stultz@linaro.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
        Len Brown <len.brown@intel.com>,
        Rafael Wysocki <rafael.j.wysocki@intel.com>,
        Eduardo Valentin <edubezval@gmail.com>, Paul Turner <pjt@google.com>,
        jacob.jun.pan@linux.intel.com
Subject: Re: [PATCH 2/4] timer: relax tick stop in idle entry
Message-ID: <20151117045721.2c565e42@yairi>
In-Reply-To: <20151117102449.GR3816@twins.programming.kicks-ass.net>
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	<20151116223210.GA21522@cloud>
	<20151116232640.GM5184@linux.vnet.ibm.com>
	<20151117014103.GA6629@x>
	<20151117025342.GP5184@linux.vnet.ibm.com>
	<564A978A.8060905@linux.intel.com>
	<20151117050403.GQ5184@linux.vnet.ibm.com>
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On Tue, 17 Nov 2015 11:24:49 +0100
Peter Zijlstra <peterz@infradead.org> wrote:

> On Mon, Nov 16, 2015 at 09:04:03PM -0800, Paul E. McKenney wrote:
> > On Mon, Nov 16, 2015 at 06:57:14PM -0800, Arjan van de Ven wrote:
> > > On 11/16/2015 6:53 PM, Paul E. McKenney wrote:
> > > >Fair point.  When in the five-jiffy throttling state, what can
> > > >wake up a CPU?  In an earlier version of this proposal, the
> > > >answer was "nothing", but maybe that has changed.
> > > 
> > > device interrupts are likely to wake the cpus.
> > 
> > OK, that I cannot help you with.  But presumably if the interrupt
> > handler does a wakeup (or similar), that is deferred to the end of
> > the throttling interval?  Timers are also deferred, including
> > hrtimers?
> 
> This throttling thing only throttles 'normal' tasks, real-time tasks
> will still run.

As an optimization or option, it might be useful to further defer the
next timer interrupt if it falls within the idle injection period. But
I guess we don't know if that timer belongs to a normal task or rt.
Also we there could be more than one 'next' timer interrupts fall into
that injection idle period.
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