Messages in this thread | | | Date | Tue, 13 Dec 2005 10:35:01 -0800 | From | Jay Lan <> | Subject | Re: [Lse-tech] [RFC][Patch 1/5] nanosecond timestamps and diffs |
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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.
How is this proposed function different from do_posix_clock_monotonic_gettime()? It calls getnstimeofday(), it also adjusts with wall_to_monotinic.
It seems to me we just need to EXPORT_SYMBOL_GPL the do_posix_clock_monotonic_gettime()?
Thanks, - jay
> > 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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