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    SubjectRe: combinatorial explosion in lockdep

    * David Miller <> wrote:

    > From: David Miller <>
    > Date: Mon, 28 Jul 2008 15:37:02 -0700 (PDT)
    > > I'm still digging on what exactly makes this happen, but I wanted to
    > > get the information out as soon as I had something useful like this.
    > As a simple hack, I tried mitigating these effects using a
    > generation-count based "visited" scheme to bypass traversing
    > lock_class chains we've already walked down.
    > It seems to work.


    Any chance to get the "cat /proc/lockdep*" output, so that we could see
    and check the expected behavior of the full graph?

    But with 128 cpus and double locking taking in the scheduler, there's
    around 127*128/2 possible combinations of cpu rq lock ordering, that's
    thousands of chains, and that takes a quadratic number of steps to
    iterate via the current algorithm - which would be in the neighborhood
    of 127^4 / 4, or about 65 million steps for each new change to the
    graph. (but it's late and i'm not sure at all about the numbers so i
    could be off by a few orders of magnitude, in either direction)

    Plus the irqsafe/softirqsafe layers multiply things too.

    Could you please also send the non-stack-iterator changes you did as
    well - that's cool stuff too!


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