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    SubjectRe: [PATCH v1 5/9] perf util: Remove a set of shadow stats static variables
    On Tue, Nov 21, 2017 at 10:03:50AM -0800, Andi Kleen wrote:
    > > all this is about switching from array to rb_list for the --per-thread case,
    > > which can be considered as a special use case.. how much do we suffer in
    > > performance with new code? how about the "perf stat -I 100", would it scale
    > > ok for extreme cases (many events in -e or -dddd..)
    >
    > rbtrees scale by log N, with N being the entries in the tree.
    >
    > Even in extreme cases, let's say 10000 events and 1000 cpus it would
    > need only 8 memory accesses and comparisons for each look up.
    > Even if we assume cache misses for all of the memory lookups,
    > at ~200ns per cache miss it's still only 1us per event, which
    > is negligible.
    >
    > In practice not all memory accesses will be misses because
    > the upper levels of the tree are almost certainly cached
    > from earlier accesses.

    sounds good, thanks

    jirka

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