Re: About ceph_clock_now()

["Adam C. Emerson" <aemerson@redhat.com>]

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On 22/01/2016, Erwan Velu wrote:
> Hey,
> 
> I've been able to continue this work and updated by branch accordingly.
> I understand the benefit of using the ceph_time work but I feel that it makes the change pretty verbose for a not a so big change (CLOCK_REALTIME vs CLOCK_MONO).
>
> This imply a change of all utime_t and makes the computations a little bit more complex to read.

There are a few changes one can use to make it less verbose. If you're not in a
header file (or inside a function), you might like to do:

using ceph::coarse_mono_clock;

(Don't do that in headers outside of functions, though.)

Then you can just do things like

auto now = mono_clock_coarse::now();

Which should be a bit less verbose.

Or even:

using cm_clock = ceph::coarse_mono_clock;

auto now = cm_clock::now();

> Does it worth the time spent on it ? If yes, I don't have any issue continuing this way.
> I'm pretty new to the project and would like to make the best PR as possible.
> So your insights on the under-work patch would be very helpful.

I think so. We definitely wnat to use monotonic clocks where appropriate. And we
can get a performance benefit from using coarse clocks where appropriate, too.
And we want to switch to the ceph_time stuff anyway just because it rules out a
whole class of bugs and integrates with standard and third-party libraries.

-- 
Senior Software Engineer           Red Hat Storage, Ann Arbor, MI, US
IRC: Aemerson@{RedHat, OFTC, Freenode}
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