Dropping "depends on SMP" for HAVE_ARM_TWD -- take 2

Afzal Mohammed afzal.mohd.ma at gmail.com
Mon Oct 5 04:49:40 PDT 2015


On Sun, Oct 04, 2015 at 10:46:52PM -0700, Sören Brinkmann wrote:
> On Sat, 2015-10-03 at 11:12AM +0100, Marc Zyngier wrote:

> > Indeed, I cannot see any code that does that in the GT driver. But if
> > you have an A9 MP, you probably want to stick to TWD, which gives you a
> > per-cpu timer instead of a global timer that will require IPIs to other
> > CPUs.
> I think the TWD only provides a clock_event device. Clocksource and
> schedclock would have to be provided by something else.

If no clocksource, sched clock is provided, default jiffies based ones
would be sufficient for single core, no ?, though not a preferred one.


> I looked at that once. IIRC, the problems are schedclock and clocksource.
> Other than a clockevent device which can be adjusted for frequency
> changes, there is (at least was) no such mechanism for clocksources and
> schedclock. Those are required to run at a stable frequency at all times

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