Why is tc_get_timecount() called two times in tc_init()?

[Konstantin Belousov]

On Tue, Oct 01, 2019 at 01:11:18PM +0200, Sebastian Huber wrote:
> Hello,
> 
> since this commit
> 
> https://github.com/freebsd/freebsd/commit/307f787e5a7f
> 
It is not very useful to pass github hashes around.

I think that the addition of the second tc_get_timecount() was done
earlier, in r95530, and there it has semi-useful comment
+  /* Warm up new timecounter. */
+  (void)newtc->tc_get_timecount(newtc);
+  (void)newtc->tc_get_timecount(newtc);

The commit message is not helpful at all.

I do not see a timecounter which would need two get_timecount() calls
to start working properly now, but I can imagine that at time it was.

I added Bruce to Cc: to may be get more context and explanation.

> tc_get_timecount() is called two times in tc_init().
> 
> /*
>   * Initialize a new timecounter and possibly use it.
>   */
> void
> tc_init(struct timecounter *tc)
> {
> [...]
> 	if (tc->tc_quality == timecounter->tc_quality &&
> 	    tc->tc_frequency < timecounter->tc_frequency)
> 		return;
> 	(void)tc->tc_get_timecount(tc);
> 	(void)tc->tc_get_timecount(tc);
> 	timecounter = tc;
> }
> 
> What is the reason for this procedure?
> 
> -- 
> Sebastian Huber, embedded brains GmbH
> 
> Address : Dornierstr. 4, D-82178 Puchheim, Germany
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> 
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