svn commit: r327423 - in head/sys: kern sys

[Colin Percival]

On 01/17/18 15:09, Gleb Smirnoff wrote:
> On Sun, Dec 31, 2017 at 09:21:01AM +0000, Colin Percival wrote:
> C>   Code for recording timestamps of events, especially function entries/exits.
> C>   This is a very primitive system, intended for use in measuring performance
> C>   during the early system boot, before more sophisticated tools like DTrace
> C>   or infrastructure like kernel memory allocation and mutexes are available.
> 
> Sorry if my question is too lame and late. Why can't you use ktr(4) tracer
> for that purpose? The discussion on freebsd-current also doesn't have answer.

I considered it, but it wasn't a good fit for a couple reasons:

1. ktr uses a circular buffer, while (since I'm looking at the boot process) I
want to fill a buffer and then stop recording.

2. I would have needed to hack up ktr in order to make it work early enough
in the boot process.  (Most obviously: When we enter hammer_time, trying to
access 'curthread' is a Bad Idea.)

Since the timestamp recording framework I needed was just a few lines of code
-- all the other commits are to add the points where timestamps are recorded,
and would have been needed even if I used ktr -- it seemed better to just add
my own code rather than coercing ktr to do what I needed.

-- 
Colin Percival
Security Officer Emeritus, FreeBSD | The power to serve
Founder, Tarsnap | www.tarsnap.com | Online backups for the truly paranoid