Messages in this thread | | | From | "Manfred Bartz" <> | Subject | Re: Anyone else interested in a high-precision monotonic counter? | Date | 05 Jan 2001 14:29:00 +1100 |
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"Christopher Friesen" <cfriesen@nortelnetworks.com> writes:
> Has anyone ever considered including a microsecond-precision > monotonically-increasing counter in the kernel? This would allow for > easy timing of alarms and such by using absolute values of when the > alarm should expire rather than a list of deltas from previous alarms. > > The thing I have in mind would store a value something like "xtime" > (maybe call it "ytime"?) in the kernel. This value would be initialized > to zero on startup, and would be incremented at the same time as > "xtime". However, while "xtime" reflects adjustments to the actual > system time (settimeofday(), date, ntp, etc.), this value would not. > Finally, it would be accessed with a system call essentially identical > to sys_gettimeofday(), only it would access "ytime" instead of "xtime" > before going down and getting the microseconds from the RTC. > > This doesn't seem to me as though it would be all that tricky to add, > and I could see it being very useful in providing a timing source that > is guaranteed to > a) be accurate to microseconds and > b) never go backwards.
Why a new system call?
regarding a: it could have microsecond resolution but not microseconds accuracy. regarding b: have you looked at the return-value of times(2) Or roll your own using setitimer(2) -- Manfred - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org Please read the FAQ at http://www.tux.org/lkml/
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