linux-kernel - Re: scheduling anomaly on uml (was: -rt doesn't compile for UML)

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Message-ID: <20071129171647.GA1326@elte.hu>
Date:	Thu, 29 Nov 2007 18:16:47 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeff Dike <jdike@...toit.com>
Cc:	Miklos Szeredi <miklos@...redi.hu>,
	user-mode-linux-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org
Subject: Re: scheduling anomaly on uml (was: -rt doesn't compile for UML)


* Jeff Dike <jdike@...toit.com> wrote:

> On Thu, Nov 29, 2007 at 11:19:40AM +0100, Miklos Szeredi wrote:
> >     date-7119  0.... 15636591us!: schedule <bash-502> (0 0)
> >     bash-502   0.... 15643908us!: schedule <date-7119> (0 0)
> >     bash-502   0.... 15646250us!: schedule <date-7120> (0 0)
> 
> How exactly did you end up getting this data?
> 
> And is there something I can read to tell what it means?

the header of /proc/latency_trace explains the format:

                 _------=> CPU#
                / _-----=> irqs-off
               | / _----=> need-resched
               || / _---=> hardirq/softirq
               ||| / _--=> preempt-depth
               |||| /
               |||||     delay
   cmd     pid ||||| time  |   caller
      \   /    |||||   \   |   /
 privoxy-12926 1.Ns1    0us : ktime_get_ts (ktime_get)

'time' is timestamp in microseconds. Then come the caller (and parent, 
or other, special parameters like the task-pid of the scheduled task). 
It's supposed to be easy to read to kernel hackers - let me know if any 
of the details is non-obvious.

for example:

> >     date-7119  0.... 15636591us!: schedule <bash-502> (0 0)

the task 'date' (pid 7119) scheduled at timestamp 15636591us, and 
switched to another task 'bash' (pid 502). Both had a default nice level 
of 0 [the (0 0) arguments].

	Ingo
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