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Date: Tue, 24 Nov 2009 12:45:15 +0100 From: Tim Blechmann <tim@...ngt.org> To: Pekka Enberg <penberg@...helsinki.fi> CC: Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org, Christoph Lameter <cl@...ux-foundation.org>, Nick Piggin <npiggin@...e.de> Subject: Re: [PATCH 3/5] slab.c: remove branch hint -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 11/24/2009 12:28 PM, Pekka Enberg wrote: > On Tue, Nov 24, 2009 at 1:20 PM, Ingo Molnar <mingo@...e.hu> wrote: >> (Pekka Cc:-ed) >> >> * Tim Blechmann <tim@...ngt.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@...ngt.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. i don't know, if there is any facility in the ftrace branch profiler to get call graph information, but i can try to manually dump backtraces in this condition path ... could be a specific situation on my machine, though ... tim - -- tim@...ngt.org http://tim.klingt.org You don't have to call it music if the term shocks you. John Cage -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) iEYEARECAAYFAksLx0kACgkQdL+4qsZfVsskOQCglFQG3eYAfdgXoOAHAGTqaLcU 8e0AoIQNbzSRxttGFaXTF3PEh5O4aGEB =3nmT -----END PGP SIGNATURE----- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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