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    SubjectRe: [PATCH] perf tools: Add a new generic section in perf.data

    * Frederic Weisbecker <fweisbec@gmail.com> wrote:

    > On Fri, Oct 16, 2009 at 09:10:46AM +0200, Ingo Molnar wrote:
    > >
    > > * Frederic Weisbecker <fweisbec@gmail.com> wrote:
    > >
    > > > +/*
    > > > + * Version 0: contains trace_info section only
    > > > + */
    > > > +struct perf_file_additionals {
    > > > + u64 version;
    > > > + struct perf_file_section trace_info;
    > > > +};
    > >
    > > i dont disagree with the change - but it would be even nicer to simply
    > > define a features bitmask, instead of a flat version - and add the
    > > trace_info section as a feature.
    > >
    > > That way it's all a lot more manageable: we dont know about versions per
    > > se, we know about features. Individual features could be developed (and
    > > backported) in a distributed way - without having to worry about a flat
    > > version model.
    > >
    > > So i'd suggest something like a bitmask in the perf.data file header:
    > >
    > > DECLARE_BITMAP(features, 256);
    > >
    > > Plus every perf version knows about the features it supports:
    > >
    > > DECLARE_BITMAP(features_supported, 256);
    > >
    > > The compatibility rule is: perf only touches attributes that belong to
    > > features it knows about.
    > >
    > > Ingo
    >
    >
    > Yeah, I've thought about that too but feared about the limitation of
    > bitweight(u64), although it's probably enough, we never know. That
    > said I can take a bunch of four u64 to draw this bitmap and 256
    > features is enough.
    >
    > Indeed that's way much better as a bitmap. Will do that instead.

    Yeah, but please reuse linux/bitmap.h instead of some open-coded array
    of 4x u64's.

    Ingo


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