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    SubjectRe: [RFC 3/4] perf, ftrace: Add new perf ioctl for function trace filter
    On Mon, Jul 18, 2011 at 05:12:33PM +0200, Frederic Weisbecker wrote:
    > On Mon, Jul 11, 2011 at 03:22:55PM +0200, Jiri Olsa wrote:
    > > As the amount of kernel functions obtained by the ftrace:function tracepoint
    > > is quite big, it's desirable to be able to set the filter on the ftrace
    > > level.
    > >
    > > Added PERF_EVENT_IOC_SET_FTRACE ioctl to be able to specify function filter
    > > for perf event. The interface is the same as for the set_ftrace_filter file.
    > >
    > > Also the same string parser is used as for the set_ftrace_filter file.
    >
    > I'm not sure I understand why an ioctl is needed for that.
    > Why not using the ftrace filter?
    >
    > The first idea was to do something like this:
    >
    > ip == func1 || ip == func2 || ....

    The part where I got stuck is when you start to combine the fields
    in the filter like:

    ip == func1 || ip_parent != func2
    ip == func1 || (ip == func2 && ip_parent != func3)

    Which is ok when all functions are enabled and ip/parent_ip fields
    are treated as values. But I'd need enable proper set of functions
    based on above filter parsing.. which might not be that easy :)

    So I thought it'd be easier to have the filter as above,
    plus you could specify the amount of traced functions with
    ioctl command.

    >
    > But that makes a too long expression. So I thought we
    > could bring support for the "+" operator and have expressions
    > like:
    >
    > ip == func1 + func2 + func3 + ....
    >
    > ip == !func1

    So would you like to have just simple filter for function event?
    (embedded into the current event filter..) like:

    ip == func1 + func2 + func3 +

    Support just one 'ip' field and whatever we got in the parameter
    we put into the ftrace filter.. ?

    thanks,
    jirka


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