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

From: Peter Zijlstra
Date: Thu Jan 12 2017 - 04:21:11 EST


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?