Messages in this thread Patch in this message | | | Date | Sun, 29 Nov 2009 12:36:34 +0100 | From | Tim Blechmann <> | Subject | Re: [PATCH 3/5] slab.c: remove branch hint |
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On 11/24/2009 12:28 PM, Pekka Enberg wrote: > 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.
when dumping the stack for the incorrectly hinted branches, i get the attached stack traces...
hth, tim
--- a/mm/slab.c +++ b/mm/slab.c @@ -3548,8 +3548,10 @@ __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 (nodeid == -1) + if (nodeid == -1) { + dump_stack(); nodeid = this_node; + }
if (unlikely(!cachep->nodelists[nodeid])) { /* Node not bootstrapped yet */
-- tim@klingt.org http://tim.klingt.org
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