Messages in this thread | | | Date | Fri, 27 Aug 2010 13:24:06 +0200 | From | Richard Cochran <> | Subject | Re: [PATCH 1/1] posix clocks: introduce syscall for clock tuning. |
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On Mon, Aug 23, 2010 at 01:41:13PM -0700, john stultz wrote: > As I mentioned in the previous mail, I agree the new functionality > (adjusting the time by an offset instantaneously) is useful, but I'd > prefer it be done initially within the existing adjtimex() interface.
But the adjtimex does not support nanosecond resolution.
> Then if the posix-time clock_id multiplexing version of adjtimex is > found to be necessary, the new syscall should be introduced, using the > same API (not all clock_ids need to support all the adjtimex modes, but > the new interface should be sufficient for NTPd to use).
Would the new syscall need to take a struct timex?
If so, I think it not worth the effort of adding a syscall. Instead, we can just add "clockid" flags into the mode field.
> There are some other conceptual issues this new syscall introduces: > > 1) While clock_adjtimex(CLOCK_REALTIME,...) would be equivalent to > adjtimex(), would clock_adjtimex(CLOCK_MONOTONIC,...) make sense? > > Given CLOCK_MONOTONIC and CLOCK_REALTIME are both based off the same > notion of time, but offset from each other, any adjustment to one clock > would be reflected in the other. However, the API would make it seem > like they could be adjusted independently.
You could adjust the frequency of either one. As a side effect, the other clock would also be adjusted.
You can only change the time offset on CLOCK_REALTIME, and that would have no effect on CLOCK_MONOTONIC.
> 2) The same issue in #1 exists for CLOCK_REALTIME/MONOTONIC_COARSE > variants. > > 3) Freq steering for MONOTONIC_RAW would defeat the purpose of the > clock_id.
If I understand correctly, MONOTONIC_RAW is just access to the hardware counter?
> 4) Does adjustments to CPU_TIME clock_ids make sense?
Don't think so.
Thanks, Richard
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