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
-john
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