Re: [RFC] exponential update_wall_time

From: john stultz
Date: Wed Sep 27 2006 - 19:13:38 EST

On Thu, 2006-09-28 at 01:04 +0200, Roman Zippel wrote:
> On Wed, 27 Sep 2006, john stultz wrote:
> > Accumulate time in update_wall_time exponentially.
> > This avoids long running loops seen with the dynticks patch
> > as well as the problematic hang" seen on systems with broken
> > clocksources.
> This is the wrong approach, second_overflow() should be called every HZ
> increment steps and your patch breaks this.

First, forgive me, since I've got a bit of a head cold, so I'm even
slower then usual. I just don't see how this patch changes the behavior.
Every second we will call second_overflow. But in the case where we
skipped 100 ticks, we don't loop 100 times. Could you explain this a bit

> There are other approaches oo accommodate dyntick.
> 1. You could make HZ in ntp_update_frequency() dynamic and thus reduce the
> frequency with which update_wall_time() needs to be called (Note that
> other clock variables like cycle_interval have to be adjusted as well).

I'm not sure how this is functionally different from what this patch

> 2. If dynticks stops the timer interrupt for a long time, it could
> precalculate a few things, e.g. it could complete the second and then
> advance the time in full seconds.

Not following this one at all.

Again, sorry for being so thick.

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