[ntp:questions] Which version of Linux works best?

unruh unruh at wormhole.physics.ubc.ca
Fri Mar 12 16:37:27 UTC 2010

On 2010-03-12, Terje Mathisen <"terje.mathisen at tmsw.no"> wrote:
> unruh wrote:
> [snip]
>> time that the serial port ioctl returned. I know on my parallel port
>> interrupt, the test I ran showed that the time between activating the
>> pin on the parallel port and the parallel port interrupt service routine
>> timestamping the interrupt was of the order of 1usec. It would be nice
>> to see what it is for the serial port. I doubt it is much more than
>> that.
> You might be wrong, and this is supposedly the reason phk started using 
> the parallel port in the first place:

I might well be wrong. 

> At least some serial ports will gate their interrupt signal to the 
> resolution of their internal clock frequency or hw polling interval, 
> which can result in multiple us's of delay.

Some of the possible interrupts ARE interrupts that come through the
clocked inputs, and thus would have to be at the clock freq. But I
thought that the serial port had at least one interrupt line that
delivered immediate interupts. But I have never looked at it to find

> OTOH, I have personally never seen this on any of my S1 servers which 
> all use the serial port.

Not sure how you would "see" that. If the interrupt were delayed by one
ms ntp would not know. It would see something only if that delay were

> Terje

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