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    SubjectRe: [patch 0/3] [Announcement] Performance Counters for Linux
    Thomas Gleixner writes:

    > We'd like to announce a brand new implementation of performance counter
    > support for Linux. It is a very simple and extensible design that has the
    > potential to implement the full range of features we would expect from such
    > a subsystem.

    Looks like the sort of thing I was thinking about a year or so ago
    when I was trying to come up with a simpler API than perfmon2.
    However, it turned out that my design, and I believe yours too, can't
    do some things that users really want to do with performance
    counters.

    One thing that this sort of thing can't do is to get values from
    multiple counters that correlate with each other. For instance, we
    would often want to count, say, L2 cache misses and instructions
    completed at the same time, and be able to read both counters at very
    close to the same time, so that we can measure average L2 cache misses
    per instruction completed, which is useful.

    Another problem is that this abstraction provides no way to deal with
    interrelationships between counters. For example, on PowerPC it is
    common to have a facility where one counter overflowing can cause all
    the other counters to freeze. I don't see this abstraction providing
    any way to handle that.

    It looks to me that your new API will be unworkable for real
    performance measurement and tuning, just like mine ended up being. :)

    Paul.


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