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    SubjectRe: [PATCH 0/3] FUTEX : new PRIVATE futexes, SMP and NUMA improvements
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    On Fri, 2007-03-16 at 10:30 +0100, Eric Dumazet wrote:
    > On Friday 16 March 2007 09:05, Peter Zijlstra wrote:
    > > On Thu, 2007-03-15 at 20:10 +0100, Eric Dumazet wrote:
    > > > Hi
    > > >
    > > > I'm pleased to present these patches which improve linux futex
    > > > performance and scalability, on both UP, SMP and NUMA configs.
    > > >
    > > > I had this idea last year but I was not understood, probably because I
    > > > gave not enough explanations. Sorry if this mail is really long...
    > >
    > > I started playing with it after your last reference to it, I have some
    > > code here (against -rt):
    > > http://programming.kicks-ass.net/kernel-patches/futex-vma-cache/
    > >
    > > Which I will post once I have the found what keeps pthread_join() from
    > > completing :-(
    > >
    > > It basically adds a per task vma lookup cache which can also activate
    > > the private logic without explicit use of the new interface.
    >
    > Hi Peter
    >
    > I dont think yet another cache will help in the general case.
    > A typical program uses many vmas at once...
    >
    > glibc has internal futexes, on a different vma than futexes declared in your
    > program. Each shared library is going to have its own vma for its data (and
    > futexes)
    >
    > (244 vmas on one kmail program for example)

    Yeah, I was just hoping a few cache entries would be enough to get the
    worst of them. A benchmark will have to tell I guess.

    > About your guess_futex_shared() thing, I miss the vma_anon() definition.

    http://programming.kicks-ass.net/kernel-patches/futex-vma-cache/vma_cache.patch

    > But if it has to walk the vmas (and take mmap_sem), you already loose the
    > PRIVATE benefit.

    It doesn't take mmap_sem, I am aware of the problems.

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