Re: Anyone else interested in a high-precision monotonic counter?

["Manfred Bartz" <md-linux-kernel@logi.cc>]

"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
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