DTrace for FreeBSD - fbt output

[John Baldwin]

On Tuesday 13 June 2006 17:36, John Birrell wrote:
> On Tue, Jun 13, 2006 at 02:15:43AM +0000, John Birrell wrote:
> > With the development as it stands at the moment, take care using the FBT
> > provider because you can easily cause the system to go kaboom. I'm still
> > trying to track down the problems there. It's not in FBT itself -- just
> > the fact that the DTrace probe context isn't allowed to call anything that
> > FBT can instrument. If that happens you will either get a reboot or a
> > double fault will leave you in kdb. I recommend only enabling a few FBT
> > probes at a time just so you know which ones could cause a fault. There is
> > no point telling me that you enabled fbt::: and the system went kaboom!
> 
> With the FBT provider as it now stands and using this script:
> 
> fbt:::entry
> {
>         @[probefunc] = count();
> }
> 
> the output after a buildworld is listed below. Check out the number of
> calls to critical_enter and critical_exit (which are listed at the bottom)!
> And for comparison, check the hardclock() count which relects 1000 Hz.

Those functions are called a lot as every spinlock ends up calling them
(including sched_lock, turnstile chain locks, sleepqueue locks, etc.)

One thing I found odd is:

>   cpu_set_fork_handler                                            608
>   kthread_create                                                  608
>   kthread_exit                                                    608

We created and destroyed 608 kernel threads during a buildworld??  This
doesn't seem right.  Were you doing the buildworld over NFS?

-- 
John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org