Re: weird Ctrl-T debug messages

On Sat, 27 Jun 2020 12:06:17 +0300
Andriy Gapon <avg_at_FreeBSD.org> wrote:

> On 27/06/2020 10:44, Li-Wen Hsu wrote:
> > On Sat, Jun 27, 2020 at 3:04 PM Hartmann, O.
> > <ohartmann_at_walstatt.org> wrote:  
> >>
> >> Running poudriere on recent CURRENT with (recent) 12-STABLE and
> >> CURRENT jails reveals a weird behaviour recently when hitting
> >> Ctrl-T:  
> > ...  
> >> Is this debug fallout from /bin/sh?  
> > 
> > It's because kern.tty_info_kstacks is on by default now:
> > 
> > https://svnweb.freebsd.org/changeset/base/362141  
> 
> May I suggest that the stack trace is printed procstat -kk style
> (single line) ? I think that the more compact output would be more
> convenient.

It's a cool feature and having it on by default on CURRENT certainly
helps to discover it, which is great. Thanks for implementing this!

I wouldn't enable it by default on RELEASE versions though, as CTRL-T
is a user interface to get status information (at least this is how I
use it personally, e.g., while running commands like dd[0], cp, mv,
poudriere etc.), not for getting debug output.

Getting debug information every time I want to get the status seems
like something that would make my user experience worse. I understand
that this can be disabled locally, but that's a bit like changing
the default syslog.conf to write messages of log level LOG_DEBUG
to /var/log/messages.

So, in the long run (before 13-RELEASE) I would prefer to disable it by
default again, but maybe alter the default sysctl.conf to contain:

# Uncomment this to show stack traces on SIGINFO (ctrl-t)
#kern.tty_info_kstacks=1

Question: Speaking of discovering the feature, wouldn't it make sense
to document this tunable on the stack(9) and/or tty(4) man page(s)?

Just my 2 cents

[0] Typical use case:

$ dd if=/dev/random of=/dev/da0 bs=1m
<presses CTRL-T>
load: 0.37  cmd: dd 32247 [running] 0.91r 0.00u 0.88s 8% 2672k
149+0 records in
149+0 records out
156237824 bytes transferred in 0.922956 secs (169279818 bytes/sec)
<presses CTRL-T again>
load: 0.42  cmd: dd 32247 [running] 2.52r 0.00u 2.46s 21% 2676k
398+0 records in
398+0 records out
417333248 bytes transferred in 2.528253 secs (165067835 bytes/sec)
...

-- 
Michael Gmelin