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    SubjectRe: [RFC][PATCH RT 1/2] futex_requeue-optimize
    Sébastien Dugué <sebastien.dugue@bull.net> wrote:
    >
    >
    >
    > In futex_requeue(), when the 2 futexes keys hash to the same bucket, there
    > is no need to move the futex_q to the end of the bucket list.
    >
    > ...
    >
    > Index: linux-2.6.16-rt20/kernel/futex.c
    > ===================================================================
    > --- linux-2.6.16-rt20.orig/kernel/futex.c 2006-05-04 10:58:38.000000000 +0200
    > +++ linux-2.6.16-rt20/kernel/futex.c 2006-05-04 10:58:55.000000000 +0200
    > @@ -835,17 +835,20 @@ static int futex_requeue(u32 __user *uad
    > if (++ret <= nr_wake) {
    > wake_futex(this);
    > } else {
    > - list_move_tail(&this->list, &hb2->chain);
    > - this->lock_ptr = &hb2->lock;
    > + /*
    > + * If key1 and key2 hash to the same bucket, no
    > + * need to requeue.
    > + */
    > + if (likely(head1 != &hb2->chain)) {
    > + list_move_tail(&this->list, &hb2->chain);
    > + this->lock_ptr = &hb2->lock;
    > + }
    > this->key = key2;
    > get_key_refs(&key2);
    > drop_count++;
    >
    > if (ret - nr_wake >= nr_requeue)
    > break;
    > - /* Make sure to stop if key1 == key2: */
    > - if (head1 == &hb2->chain && head1 != &next->list)
    > - head1 = &this->list;
    > }
    > }

    For some reason I get a reject when applying this. Which is odd, because I
    see no differences in there. Oh well - please try to work out what went
    wrong and double-check that the patch which I applied still makes sense.

    Should the futex code be using hlist_heads for that hashtable?
    -
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