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

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Date:   Thu, 12 Jan 2017 10:20:37 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Janakarajan Natarajan <Janakarajan.Natarajan@....com>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Subject: Re: [PATCH 2/3] perf/x86/amd/uncore: Dynamically allocate uncore
 counters

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@....com>
> ---
>  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?