Hi,
In playing with an HPET device, I noticed that
kernel/timer.c:is_better_time_interpolator() is completely non-symmetric
in the timer it returns. The test is simply:
return new->frequency > 2*time_interpolator->frequency ||
(unsigned long)new->drift < (unsigned long)time_interpolator->drift;
Given two timers:
(a) 1.5GHz, 750ppm
(b) 250Mhz, 500ppm
the resulting "better" timer is completely dependent on the order
they're passed in. For example, (a),(b) = (b); (b),(a) = (a).
What are we really looking for in a "better" timer? There are at
least 4 factors that I can think of that seem important to determining a
better clock:
* resolution (frequency)
* accuracy (drift)
* access latency (may be non-uniform across the system?)
* jitter (monotonically increasing)
How can we munge these all together to come up with a single goodness
factor for comparison? There's probably a thesis covering algorithms to
handle this. Anyone know of one or have some good ideas? Thanks,
Alex
--
Alex Williamson HP Linux & Open Source Lab
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
| |
 |