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SubjectRe: [BUG?] tracing/function_graph: set_graph_function was broken from 2.6.36-rc2
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On Thu, 2011-01-20 at 02:55 +0800, wu zhangjin wrote:
> Hi, Steve
>
> Zhiping Zhong reported a problem about set_graph_function: whenever
> users configure the entries through the tracing/set_graph_function
> interface, the tracing result always include the other functions which
> are not configured through the interfaces, and most of the tracing
> result we can see are the irq related functions, which means
> set_graph_function doesn't work as expects.

It does, but you need to disable irq tracing:

echo 0 > /debug/tracing/options/funcgraph-irqs
Perhaps I'll make this the default :-/

-- Steve

>
> I have done some investigation, in the *ftrace_graph_entry ->
> trace_graph_entry() function, there is checking like this:
>
> [snip]
> /* trace it when it is-nested-in or is a function enabled. */
> if (!(trace->depth || ftrace_graph_addr(trace->func)) ||
> ftrace_graph_ignore_irqs())
> return 0;
> [snip]
>
> and:
>
> static inline int ftrace_graph_ignore_irqs(void)
> {
> if (!ftrace_graph_skip_irqs)
> return 0;
>
> return in_irq();
> }
>
> and:
>
> /* When set, irq functions will be ignored */
> static int ftrace_graph_skip_irqs;
>
> As we can see above, ftrace_graph_skip_irqs is initialized as 0, then,
> ftrace_graph_ignore_irqs() will return 0 by default, as a result, the
> checking in trace_graph_entry() will always be false, then every
> function will be traced whenever the set_graph_function is configured,
> so, this may be the cause.
>
> A quick fix looks like this:
>
> /* trace it when it is-nested-in or is a function enabled. */
> - if (!(trace->depth || ftrace_graph_addr(trace->func)) ||
> - ftrace_graph_ignore_irqs())
> + if (!(trace->depth || ftrace_graph_addr(trace->func) ||
> + !ftrace_graph_ignore_irqs()))
> return 0;
>
> And as the git log shows, the ftrace_graph_ignore_irqs() function was
> added from the following commit:
>
> tracing: Do not trace in irq when funcgraph-irq option is zero
>
> Regards,
> Wu Zhangjin




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