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