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

[Matt Helsley <matthltc@us.ibm.com>]

On Tue, 2005-12-13 at 10:35 -0800, Jay Lan 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.
> 
> 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

Ah, yes. I should've searched for gettime rather than gettimeofday when
I was looking for a suitable function.

Two minor differences exist:

1) getnstimestamp does not fetch an unused copy of jiffies_64
2) getnstimestamp uses and advertises an explicit maximum resolution

	I don't think either of these really matter so I'll post a series of
patches:

1) EXPORTing (_SYMBOL_GPL) do_posix_clock_monotonic_gettime()
2) using do_posix_clock_monotonic_gettime() as a timestamp
3) removing getnstimestamp()

Thanks,
	-Matt Helsley