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    SubjectRe: [patch] Latency Tracer, voluntary-preempt-2.6.8-rc4-O6

    * Andi Kleen <ak@muc.de> wrote:

    > > > > yeah - kallsyms_lookup does a linear search over thousands of symbols.
    > > > > Especially since /proc/latency_trace uses it too it would be worthwile
    > > > > to implement some sort of binary searching.
    > > >
    > > > Or just stick some cond_sched()s in there. It was designed to be slow,
    > > > but there are no locking issues.
    > >
    > > the speedup would be important: even on a 2GHz box reading 10,000 trace
    > > entries takes a couple of seconds.
    >
    > That's because you're abusing it - it was never designed to process
    > that much data.

    i'm not abusing it. Linear searching of 20 thousand symbols is a gross
    first-approximation algorithm no matter what. Yes, most users of the
    symbols dont care about performance. And i'm not complaining at all, i'm
    just pointing out the reason why e.g. printing a simple stack backtrace
    can take milliseconds.

    > With binary search you would need to backward search to find the stem
    > for the stem compression. It's probably doable, but would be a bit
    > ugly I guess.

    yeah. Maybe someone will find the time to improve the algorithm. But
    it's not a highprio thing.

    Ingo
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