linux-kernel - Re: [PATCH] hrtimer: increase clock min delta threshold while interrupt hanging

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Date:	Mon, 22 Dec 2008 10:24:51 +0100
From:	"Frédéric Weisbecker" <fweisbec@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Frans Pop" <elendil@...net.nl>, tglx@...utronix.de,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hrtimer: increase clock min delta threshold while interrupt hanging

2008/12/22 Ingo Molnar <mingo@...e.hu>:
>
> * Frédéric Weisbecker <fweisbec@...il.com> wrote:
>
>> > Also, there's min_delta doubling in tick_dev_program_event() itself
>> > too - that interacts with the irq-overload logic:
>> >
>> > +       dev->min_delta_ns = (unsigned long)try_time.tv64 * 3;
>> >
>> >        Ingo
>>
>> That's what I explained above, the doubling of min delta in
>> tick_dev_program_event() is never reached in my case. And moreover I'm
>> not sure it is ever reached whatever the call sites of
>> tick_dev_program_event() unless min delta has a very low value...
>
> yeah, that looks all rather messy and probably ineffective. Thomas, mind
> to take a look?
>
> Frederic's patch solves a real timer-irq-overload extreme situation so i
> find it rather valuable. Maybe we should do Frederic's patch as-is, have
> the 'softer' min_delta behavior for the usual hrtimer codepaths - and the
> more agressive one for the timer tick only?
>
>        Ingo
>

Oh a little thing.
I wonder if 5 iterations to notice a hang is not too low for embedded
systems on certain
situations.... Since embedded systems could need high resolution
timers for real time....

Actually perhaps 10 iterations would be more reasonable....
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