On Wed, Dec 27, 2017 at 9:38 PM, Keith Packard <[email protected]> wrote:
> Jeffrey Smith <[email protected]> writes:
>
>> GetTimeInMillis uses the CLOCK_MONOTONIC_COARSE clock if
>> available and the precision is high enough. That clock is supposed
>> to be more efficient to query than CLOCK_MONOTONIC (at the cost
>> of being less precise). So implementing GetTimeInMillis by calling
>> GetTimeInMicros could mean spending extra time to get higher
>> precision, just to spend more time (for the division) throwing it
>> away.
>
> Good point. So, we want to use CLOCK_MONOTONIC_COARSE for Millis and
> CLOCK_MONOTONIC for Micros. That seems like a fine plan. I guess what
> I'm getting at is that these two functions should return a value in the
> same universe at least, so we should either be using the two MONOTONIC
> clocks, or we should be using another clock, but we shouldn't be mixing
> MONOTONIC and REALTIME clocks?
Agreed. With this patch, only these (milli clock , micro clock)
pairings should occur...
if clockid is forced:
(forced clockid , forced clockid)
else if coarse clock is available (Linux-specific, since 2.6.32) and
has 1ms or finer resolution:
(CLOCK_MONOTONIC_COARSE , CLOCK_MONOTONIC)
else if monotonic clock is available:
(CLOCK_MONOTONIC , CLOCK_MONOTONIC)
else:
(~0L , ~0L) interpreted to mean use gettimeofday
Also, the next patch changes the final pairing to:
(CLOCK_REALTIME , CLOCK_REALTIME)
>
> --
> -keith
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