Re: rtc: lost some interrupts at 256Hz

[linux-os (Dick Johnson)]

On Thu, 20 Apr 2006, Michael Monnerie wrote:

> When you google for such messages, you can find a lot of people asking,
> but nobody seems to have an answer. That's why I ask this list, where
> the Godfathers Of Linux reside, and maybe someone hears my prayer and
> could explain us sheep what you should do in such a case. Increase the
> HZ from 250 to 1000, or decrease to 100? Or maybe setting the
> preemption model from server to voluntary or preemptible? Or is that
> whining to be ignored, and if yes, what is this message for at all?
>
> Please give us wisdom, and we will spread your word. Amen.
>
> Answers please per PM, I'm not on this list.
>

If you are losing interrupts at 256 Hz, you have either/or:
(1) Some very BAD driver that is disabling interrupts for way too long.
(2) Some very slow CPU (like 40 Mhz) that is being overwhelmed by a lot of
network interrupt activity.

The last time I measured, with a 400 MHz, '486 machine, Linux could
handle 50,000 interrupts per second off the printer port, with the
lowest priority interrupt (IRQ7). The work, within the interrupt was
to toggle a bit in memory and write it back to the printer data port.

This was used to show latency (with a scope) and log any missed
interrupts of which there were none.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.16.4 on an i686 machine (5592.89 BogoMips).
Warning : 98.36% of all statistics are fiction, book release in April.
_


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