Messages in this thread | | | Subject | Re: [Lse-tech] [RFC][Patch 1/5] nanosecond timestamps and diffs | From | john stultz <> | Date | Mon, 12 Dec 2005 12:07:14 -0800 |
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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.
thanks -john
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