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
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