Re: [Lse-tech] [RFC][Patch 1/5] nanosecond timestamps and diffs

[George Anzinger <george@mvista.com>]

john stultz wrote:
> On Mon, 2005-12-12 at 20:00 +0000, Shailabh Nagar wrote:
>
> > john stultz wrote:
> >
> > > On Mon, 2005-12-12 at 19:31 +0000, Shailabh Nagar wrote:
> > >
> > >
> > > > Christoph Lameter wrote:
> > > >
> > > >
> > > > > On Wed, 7 Dec 2005, Shailabh Nagar wrote:
> > > > >
> > > > > > +void getnstimestamp(struct timespec *ts)
> > > > >
> > > > > There is already getnstimeofday in the kernel.
> > > >
> > > > Yes, and that function is being used within the getnstimestamp() being proposed.
> > > > However, John Stultz had advised that getnstimeofday could get affected by calls to
> > > > settimeofday and had recommended adjusting the getnstimeofday value with wall_to_monotonic.
> > > >
> > > > John, could you elaborate ?
> > >
> > > I think you pretty well have it covered. 
> > >
> > > getnstimeofday + wall_to_monotonic should be higher-res and more
> > > reliable (then TSC based sched_clock(), for example) for getting a
> > > timestamp.
> > >
> > > There may be performance concerns as you have to access the clock
> > > hardware in getnstimeofday(), but there really is no other way for
> > > reliable finely grained monotonically increasing timestamps.
>
>
> > Thanks, that clarifies. I guess the other underlying concern here would be whether these
> > improvements (in resolution and reliability) should be going into getnstimeofday()
> > itself (rather than creating a new func for the same) ? Or is it better to leave
> > getnstimeofday as it is ?
>
>
> No, getnstimeofday() is very much needed to get a nanosecond grained
> wall-time clock, so a new function is needed for the monotonic clock.
>
> In my timeofday re-work I have used the name "get_monotonic_clock()" and
> "get_monotonic_clock_ts()" for basically the same functionality
> (providing a ktime and a timespec respectively). You might consider
> naming it as such, but resolving these naming collisions shouldn't be
> too difficult either way.

Indeed.  Lets use a name with "monotonic" in it, please.  And, 
possibly not "clock".  How about get_nsmonotonic_time() or some such?


--
George Anzinger   george@mvista.com
HRT (High-res-timers):  http://sourceforge.net/projects/high-res-timers/
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