Re: [PATCH 2/4] timer: relax tick stop in idle entry

From: Jacob Pan
Date: Tue Nov 17 2015 - 07:57:51 EST

On Tue, 17 Nov 2015 11:24:49 +0100
Peter Zijlstra <peterz@xxxxxxxxxxxxx> 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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