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

David Woolley david at ex.djwhome.demon.invalid
Fri Mar 12 08:24:02 UTC 2010


unruh wrote:
> On 2010-03-11, Hal Murray <hal-usenet at ip-64-139-1-69.sjc.megapath.net> wrote:
>>>> Modern Linux kernels don't support PPS in the sense of RFC-whateveritis.
>>>>
>>>> There is support for an ioctl that says "wake me up when a modem signal changes".
>>>> gpsd uses that to provide PPS support.  I don't have any data.
>>> I believe but am not sure, that that uses an interrupt.
>> I think so.  But the point is that with the PPS support, the
>> kernel grabs a timestamp in the interrupt routine.  The ioctl
> 
> So? The interrupt still takes the same time to be activated. On a GHZ
> system, there is enough time in 1usec to run 1000 commands, and it is
> hard to imagine that many being used to return the ioctl. I have worried

That's 1000 machine cycles, not 1000 instructions.  On modern systems, 
I'm not sure that 1000 cycles isn't a typical time for a system call on 
modern, high level language progammed, bloatware.  (I seem to remember 
hand coding an ISR in assembler to a budget of 100 instructions (for 
68000) and it not being that easy.)




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