git: 4c0bc591466f - main - man9: add hz(9) and hardclock(9)

[Warner Losh]

> On Jun 18, 2021, at 9:18 AM, John Baldwin <jhb at FreeBSD.org> wrote:
> 
> On 6/18/21 7:43 AM, Warner Losh wrote:
>> The branch main has been updated by imp:
>> URL: https://cgit.FreeBSD.org/src/commit/?id=4c0bc591466fd2731ba892269260b7dab74cfbad
>> commit 4c0bc591466fd2731ba892269260b7dab74cfbad
>> Author:     Warner Losh <imp at FreeBSD.org>
>> AuthorDate: 2021-06-18 14:39:42 +0000
>> Commit:     Warner Losh <imp at FreeBSD.org>
>> CommitDate: 2021-06-18 14:42:51 +0000
>>     man9: add hz(9) and hardclock(9)
>>          Document aspects of system time keeping. Hz is the nominal rate that we
>>     interrupt the system and is known and the 'tick' period of 1 / hz.
>>     hardclock is the routine that does various bits of timekeeping.  stathz
>>     and profhz are documented as historical relics that are deprecated
>>     and replaced by hwpmc.4 and others.
>>          Reviewed by:            phk@, mav@ and gnn@ (previous version)
>>     Obtained from:          hardclock.9 from NetBSD (with FreeBSD adjustments)
>>     Sponsored by:           Netflix
>>     Differential Revision:  https://reviews.freebsd.org/D30802
> 
> The comments about stathz are wrong.  While profhz is obsolete and replaced by
> hwpmc, statclock is not.  statclock is used to implement getrusage(), %CPU in
> ps(1), and kern.cp_time (global and per-CPU stats for CPU usage breakdown you
> see in top(1) for example).  hwpmc doesn't replace any of those.  OTOH, it's
> also true that there's no real reason for anything outside of the actual timer
> code to use stathz (or even profhz) unlike 'hz' which is still used to set
> timeout tick values.

Thanks. All that had been blotted out of my mind somehow :(.

I’ll update and include you on the review.

Warner

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