Re: preemption and rwsems (was: Re: missing madvise functionality)

Andrew Morton
2007-04-05T20:38:11Z

On Thu, 5 Apr 2007 21:11:29 +0200
Ingo Molnar <mingo@elte.hu> wrote:

>
> * David Howells <dhowells@redhat.com> wrote:
>
> > But short of recording the lock sequence, I don't think there's anyway
> > to find out for sure. printk probably won't cut it as a recording
> > mechanism because its overheads are too great.
>
> getting a good trace of it is easy: pick up the latest -rt kernel from:
>
> http://redhat.com/~mingo/realtime-preempt/
>
> enable EVENT_TRACING in that kernel, run the workload
> and do:
>
> scripts/trace-it > to-ingo.txt
>
> and send me the output.

Did that - no output was generated. config at
http://userweb.kernel.org/~akpm/config-akpm2.txt

> It will be large but interesting. That should
> get us a whole lot closer to what happens. A (much!) more finegrained
> result would be to also enable FUNCTION_TRACING and to do:
>
> echo 1 > /proc/sys/kernel/mcount_enabled
>
> before running trace-it.

Did that - still no output.

I did get an interesting dmesg spew: