Subject: re: Proposed changes to cc_microset().
To: matthew green <>
From: Frederick Bruckman <>
List: tech-kern
Date: 07/08/2004 11:13:43
On Fri, 9 Jul 2004, matthew green wrote:

>   > considering you can end up at less than 1/2 the clock that means you'll
>   > be more than half a second out by the next second.  seems pretty severe,
>   > ie, it needs to be handled correctly...  at 10 second interval, you'd
>   > end up all over the place...
>   Remember, this isn't overall timekeeping, just sub-second
>   timekeeping. Running at half-speed for 10 seconds just means you'll be
>   off by as much as a second during that interval, not that you'll
>   accumulate overall drift.
> i understand that.  i just don't see why it's even remotely
> acceptable...  acceptable in that we say "don't fix" rather than
> "fix, but it's not really a big problem."
> (i'm not sure i understand your 10 second comment.  if the cycle
> calibration is going to be increased from 1 second to 10, won't
> eg a banias 1.4ghz running a 600mhz be about 6 seconds wrong at
> the extreme?)

No, because the cycle counter only interpolates between seconds, 
currently. (With my proposed change, it would be something like 1/10 
second minimum.) So the most clock_gettime() could be off would be 1/2 
second. I think we should attempt to correct it, nonetheless, but 
there are other challenges to getting ntpd to work properly with a 
laptop that can change frequency or even go to sleep, so I wouldn't 
expect much.