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doc: update mmiotrace doc to current status 

Signed-off-by: Pekka Paalanen <pq@iki.fi>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Pekka Paalanen 2008-05-12 21:21:03 +02:00 committed by Thomas Gleixner
parent e0fd5c2fa1
commit 6f6f394d9c
1 changed files with 18 additions and 7 deletions
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25
Documentation/tracers/mmiotrace.txt
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@ -25,7 +25,8 @@ Mmiotrace feature is compiled in by the CONFIG_MMIOTRACE option. Tracing is
disabled by default, so it is safe to have this set to yes. SMP systems are
supported, but tracing is unreliable and may miss events if more than one CPU
is on-line, therefore mmiotrace takes all but one CPU off-line during run-time
activation [not implemented].
activation. You can re-enable CPUs by hand, but you have been warned, there
is no way to automatically detect if you are losing events due to CPUs racing.
Usage Quick Reference
@ -37,7 +38,7 @@ $ cat /debug/tracing/trace_pipe > mydump.txt &
Start X or whatever.
$ echo "X is up" > /debug/tracing/marker
$ echo none > /debug/tracing/current_tracer
Check kernel log.
Check for lost events.
Usage
@ -67,12 +68,22 @@ do.
Shut down mmiotrace (requires root privileges):
$ echo none > /debug/tracing/current_tracer
The 'cat' process exits. If it does not, kill it by 'fg' and pressing ctrl+c.
The 'cat' process exits. If it does not, kill it by issuing 'fg' command and
pressing ctrl+c.
[This feature is not implemented yet!]
Check your kernel log. If there are messages about mmiotrace losing events,
this is due to buffer overrun, and the trace is incomplete. You should enlarge
the buffers and try again. [How?]
Check that mmiotrace did not lose events due to a buffer filling up. Either
$ grep -i lost mydump.txt
which tells you exactly how many events were lost, or use
$ dmesg
to view your kernel log and look for "mmiotrace has lost events" warning. If
events were lost, the trace is incomplete. You should enlarge the buffers and
try again. Buffers are enlarged by first seeing how large the current buffers
are:
$ cat /debug/tracing/trace_entries
gives you a number. Approximately double this number and write it back, for
instance:
$ echo 128000 > /debug/tracing/trace_entries
Then start again from the top.
If you are doing a trace for a driver project, e.g. Nouveau, you should also
do the following before sending your results: