Messages in this thread | | | Date | Fri, 16 Jan 2009 23:59:48 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 0/2] ftrace: updates to tip |
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* Ingo Molnar <mingo@elte.hu> wrote:
> > I was afraid you would say that :-) > > > > Yes, we could add something to do this. It would take some thought on > > a good api, and implementation. This is not an easy task by any means. > > We need a way to map between a function call and a tracer, where a > > function call can call more than one tracer. > > Note that some other things could be consolidated under per function > metadata: for example set_graph_function - which really is a per > function attribute too. Plus a lot of new things would be enabled i > think.
a few other things that could be per-function attributes:
- Using function trace 'limits': trace a function 50 times and dont trace it afterwards. Each invocation of that function decreases the remaining-count by one. For example:
echo 'btrfs_join_transaction:#2' >> set_ftrace_filter
Would specify that we generate two trace entries of btrfs_join_transaction(), then stop tracing this function.
- Using function-triggered tracing: a function could be specified (via a filter format extension) to act as a 'start tracing' trigger. Another extension would be 'stop tracing' trigger.
For example:
echo 'btrfs_join_transaction:+' >> set_ftrace_filter echo 'btrfs_commit_transaction:-' >> set_ftrace_filter
The '+' is a start-tracing trigger condition, the '-' is a stop-tracing trigger condition. All function calls between btrfs_join_transaction() and btrfs_commit_transaction() would be traced.
The two could be combined - to generate the trace of a single btrfs transaction, one could do:
echo 0 > tracing_enabled echo 'btrfs_join_transaction:+#1' >> set_ftrace_filter echo 'btrfs_commit_transaction:-#1' >> set_ftrace_filter echo 1 > tracing_enabled
Other extensions are possible too:
- Trace length triggers. For example one could do:
echo 'btrfs_join_transaction:+*#10' >> set_ftrace_filter
To trace 10 function calls [allowed by current filter settings] after the first btrfs_join_transaction() call - and stop tracing after those 10 trace entries.
This would allow the creation of "surgical" one-time traces - of events and functions one is specifically interested in.
Ingo
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