Re: [PATCH 3/5] slab.c: remove branch hint
From: Pekka Enberg
Date: Tue Nov 24 2009 - 06:29:00 EST
On Tue, Nov 24, 2009 at 1:20 PM, Ingo Molnar <mingo@xxxxxxx> wrote:
> (Pekka Cc:-ed)
>
> * Tim Blechmann <tim@xxxxxxxxxx> 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@xxxxxxxxxx>
>> ---
>> 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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