Re: [RFC] timer_interrupt: Avoid device timeouts by freezing time if system froze

From: Christoph Lameter <clameter_at_engr.sgi.com>
Date: 2005-09-20 07:38:05
On Mon, 19 Sep 2005, David Mosberger-Tang wrote:

> On 9/19/05, Christoph Lameter <clameter@engr.sgi.com> wrote:
> 
> > Doing two ticks per interrupt may cause hardware to fail that relies on
> > the interval accurately being observed. I.e. lets say we have a device
> > that typically responds after 10 ticks but times out after 15.
> > 
> > If we use 2 ticks per interrupt then we will timeout after 15/2 = 7 ticks
> > before the device had a chance to do anything.
> 
> You're forgetting that the real time has already passed!

I did not think about the freeze occurring in this interval.

Think about what happens if the timeout is scheduled after the system has 
been unfrozen while the 2 ticks per tick hack is active. 

> > I think all these additional tricks just make the situation worse. My
> > patch is already a bad hack and adding more logic just makes follow-on
> > failures difficult to analyze. I'd say the cleanest solution is still to
> > stick with freezing time. I also do not feel too enthusiastic about
> > abusing the time interpolator tuning logic for compenstation.
> 
> It was you who suggested to use the time interpolator logic.  My
> approach would have been just to keep track of the "deficit" in the
> timer interrupt handler.

I suggested it because it does just involve removing a statement. Your 
approach would involve adding even more logic to the timer interrupt.
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Received on Tue Sep 20 07:41:00 2005

This archive was generated by hypermail 2.1.8 : 2005-09-20 07:41:15 EST