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SubjectRe: Re: Clock
Hi Stephen.

>> The obvious problem is that the clock will wrap round faster if
>> it's ticking at a higher rate. I believe this is being looked
>> into by some of the senior kernel hackers at the moment, for
>> various reasons.

> It was being looked at. The 2.2 kernels should now be OK when
> the jiffies counter wraps.

I havenae seen any comments re this being definately fixed, and
haven't had reason to change HZ on my systems, so I will plead
ignorance of the current status.

As you appear to be better informed than me, can you answer a few
questions on this subject please?

1. There is presumably a maximum rate to which HZ can be set that
is dictated by the hardware. What is it?

2. There is presumably also a separate maximum rate to which HZ
can be set before the timer interrupt routine starts taking
too large a proportion of the inter-timer-interrupt intervals.
This will of course be dependant on the processor and its
speed, but is there any sort of formula to determine what this
will be for any given processor?

3. Am I right in thinking that the jiffies counter is a 32-bit
counter? If so, would I be right in thinking that the maximum
interval that can be measured is (2^32-1.0)/HZ seconds ?

If I'm right, then the above between them will set the maximum rate to
which HZ can be set on any given machine.

Comments?

Best wishes from Riley.

+----------------------------------------------------------------------+
| There is something frustrating about the quality and speed of Linux |
| development, ie., the quality is too high and the speed is too high, |
| in other words, I can implement this XXXX feature, but I bet someone |
| else has already done so and is just about to release their patch. |
+----------------------------------------------------------------------+
* ftp://ftp.MemAlpha.cx/pub/rhw/Linux
* http://www.MemAlpha.cx/kernel.versions.html

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