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    SubjectRe: [PATCH 3/5] slab.c: remove branch hint
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    On Tue, Nov 24, 2009 at 1:20 PM, Ingo Molnar <mingo@elte.hu> wrote:
    > (Pekka Cc:-ed)
    >
    > * Tim Blechmann <tim@klingt.org> wrote:
    >
    >> branch profiling on my nehalem machine showed 99% incorrect branch hints:
    >>
    >>    28459  7678524  99 __cache_alloc_node             slab.c
    >>   3551
    >>
    >> Signed-off-by: Tim Blechmann <tim@klingt.org>
    >> ---
    >>  mm/slab.c |    2 +-
    >>  1 files changed, 1 insertions(+), 1 deletions(-)
    >>
    >> diff --git a/mm/slab.c b/mm/slab.c
    >> index f70b326..4125fcd 100644
    >> --- a/mm/slab.c
    >> +++ b/mm/slab.c
    >> @@ -3548,7 +3548,7 @@ __cache_alloc_node(struct kmem_cache *cachep,
    >> gfp_t flags, int nodeid,
    >>       slab_irq_save(save_flags, this_cpu);
    >>       this_node = cpu_to_node(this_cpu);
    >> -     if (unlikely(nodeid == -1))
    >> +     if (nodeid == -1)
    >>               nodeid = this_node;
    >>       if (unlikely(!cachep->nodelists[nodeid])) {

    That sounds odd to me. Can you see where the incorrectly predicted
    calls are coming from? Calling kmem_cache_alloc_node() with node set
    to -1 most of the time could be a real bug somewhere.
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