Re: [PATCH 5/7] perf: Optimise topology iteration

[Borislav Petkov]

Adding Andreas since this is his code.

On Tue, Jan 04, 2011 at 07:06:16AM -0500, Peter Zijlstra wrote:
> On Mon, 2010-12-27 at 23:38 +0800, Lin Ming wrote:
> > Currently we iterate the full machine looking for a matching core_id/nb
> > for the percore and the amd northbridge stuff , using a smaller topology
> > mask makes sense. 
> > 
> > Signed-off-by: Lin Ming <ming.m.lin@xxxxxxxxx>
> > ---
> >  arch/x86/kernel/cpu/perf_event_amd.c   |    2 +-
> >  arch/x86/kernel/cpu/perf_event_intel.c |    2 +-
> >  2 files changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/x86/kernel/cpu/perf_event_amd.c b/arch/x86/kernel/cpu/perf_event_amd.c
> > index 67e2202..5a3b7b8 100644
> > --- a/arch/x86/kernel/cpu/perf_event_amd.c
> > +++ b/arch/x86/kernel/cpu/perf_event_amd.c
> > @@ -323,7 +323,7 @@ static void amd_pmu_cpu_starting(int cpu)
> >  	nb_id = amd_get_nb_id(cpu);
> >  	WARN_ON_ONCE(nb_id == BAD_APICID);
> >  
> > -	for_each_online_cpu(i) {
> > +	for_each_cpu(i, topology_core_cpumask(cpu)) {
> >  		nb = per_cpu(cpu_hw_events, i).amd_nb;
> >  		if (WARN_ON_ONCE(!nb))
> >  			continue;
> 
> Borislav, is topology_core_cpumask() the right mask for northbridge_id
> span? I could imagine Magny-Cours would have all 12 cores in the
> core_cpumask() and have the node_mask() be half that.

So, topology_core_cpumask() or cpu_core_mask() both are cpu_core_map
which represents the socket mask. I.e., on a multisocket cpu you'll have
in it all the cores on one socket. A 12-cores Magny-Cours contains two
internal northbridges and this mask will have 12 bits set.

AFAICT, you want to iterate over the cores on a single node here
(an internal node in the Magny-Cours case) so for this we have the
llc_shared_map. See near the top of cache_shared_cpu_map_setup() in
<arch/x86/kernel/cpu/intel_cacheinfo.c> for an example.

node_mask() is roughly the same but contains correct info only with
CONFIG_NUMA on and correct SRAT table on the system.

HTH.

-- 
Regards/Gruss,
Boris.

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