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

[George Anzinger <george@mvista.com>]

Shailabh Nagar wrote:
> 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
>>
> 
> 
> Hmmm. Looks like do_posix_clock_monotonic_gettime will suffice for this patch.
> 
> Wonder why the clock parameter to do_posix_clock_monotonic_get is needed ?

Because it is called indirectly by the table driven posix clocks and 
timers code where the clock, usually, is needed.

> Doesn't seem to be used.
> 
> Any possibility of these set of functions changing their behaviour ?

Always :), but things are pretty stable now.  Might want to add a 
comment that it is being used outside of the posix "box".


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