[PATCH -rt 0/3] Make trace_freerunning work; Take 2

[Karsten Wiese <fzu@wemgehoertderstaat.de>]

Am Dienstag, 5. Dezember 2006 23:10 schrieb Ingo Molnar:
> 
> freerunning should behave the same way with regard to latency 
> measurement. I.e. report_latency() is still needed, and the kernel will 
> thus do a maximum search over all traces triggered via start/stop.
> 
> the difference is in the recording of the last-largest-latency:
> 
> - with !freerunning, the tracer stops recording after MAX_TRACE entries, 
>   i.e. the "head" of the trace is preserved in the trace buffer.
> 
> - with freerunning, the tracer never stops, it 'wraps around' after 
>   MAX_TRACE entries and starts overwriting the oldest entries. I.e. the  
>   "tail" of the trace is preserved in the trace buffer.
> 
> depending on the situation, freerunning or !freerunning might be the 
> more useful mode.
> 
> but there should be no difference in measurement.

Following 3 patches try to implement the above.

Tested on a UP only after this incantation:
	echo 0 > /proc/sys/kernel/wakeup_timing
	echo 1 > /proc/sys/kernel/trace_enabled
	echo 1 > /proc/sys/kernel/trace_user_triggered

and for half of tests:
	echo 1 > /proc/sys/kernel/trace_freerunning
or
	echo 0 > /proc/sys/kernel/trace_freerunning
.

      Karsten