Re: [PATCH 2/3] perf/x86/amd/uncore: Dynamically allocate uncore counters

[Natarajan, Janakarajan]

On 1/12/2017 3:20 AM, Peter Zijlstra wrote:
> On Wed, Jan 11, 2017 at 10:02:17AM -0600, Janakarajan Natarajan wrote:
> > This patch updates the AMD uncore driver to support AMD Family17h
> > processors. In Family17h, there are two extra last level cache counters.
> > The counters are, therefore, allocated dynamically based on the family.
> >
> > The cpu hotplug up callback function is refactored to better manage
> > failure conditions.
> >
> > Signed-off-by: Janakarajan Natarajan <Janakarajan.Natarajan@xxxxxxx>
> > ---
> >   arch/x86/events/amd/uncore.c | 141 +++++++++++++++++++++++++++++++------------
> >   1 file changed, 104 insertions(+), 37 deletions(-)
> >
> > diff --git a/arch/x86/events/amd/uncore.c b/arch/x86/events/amd/uncore.c
> > index 24c8537..7ab92f7 100644
> > --- a/arch/x86/events/amd/uncore.c
> > +++ b/arch/x86/events/amd/uncore.c
> > @@ -22,13 +22,16 @@
> >   
> >   #define NUM_COUNTERS_NB		4
> >   #define NUM_COUNTERS_L2		4
> > -#define MAX_COUNTERS		NUM_COUNTERS_NB
> > +#define NUM_COUNTERS_L3		6
> >   
> >   #define RDPMC_BASE_NB		6
> >   #define RDPMC_BASE_LLC		10
> >   
> >   #define COUNTER_SHIFT		16
> >   
> > +static int num_counters_llc;
> > +static int num_counters_nb;
> > +
> >   static HLIST_HEAD(uncore_unused_list);
> >   
> >   struct amd_uncore {
> > @@ -40,7 +43,7 @@ struct amd_uncore {
> >   	u32 msr_base;
> >   	cpumask_t *active_mask;
> >   	struct pmu *pmu;
> > -	struct perf_event *events[MAX_COUNTERS];
> > +	struct perf_event **events;
> >   	struct hlist_node node;
> >   };
> Why bother with the dynamic allocation crud? Why not simply set
> MAX_COUNTERS to 6 and be happy?
My reasoning behind using dynamic allocation was to prevent memory from
being allocated when not needed on a per cpu basis. If memory isn't a
consideration, I can send a v2 without the dynamic memory allocation.