Re: [PATCH] perf/x86/amd/uncore: turn amd_uncore_ctx events into a flexible array

[Ian Rogers]

On Fri, May 22, 2026 at 6:19 PM Rosen Penev <rosenp@xxxxxxxxx> wrote:
>
> The events pointer was kzalloc_node()'d immediately after the parent
> struct allocation, with the count (pmu->num_counters) trivially
> available beforehand.  Move events to the struct tail as a flexible
> array member and fold the two allocations into a single kzalloc_node()
> with struct_size(), dropping the separate kfree(ctx->events) in the
> free path.
>
> Assisted-by: Claude:Opus-4.7
> Signed-off-by: Rosen Penev <rosenp@xxxxxxxxx>
> ---
>  arch/x86/events/amd/uncore.c | 15 +++------------
>  1 file changed, 3 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/events/amd/uncore.c b/arch/x86/events/amd/uncore.c
> index 05cff39968ec..0e265fc1fef8 100644
> --- a/arch/x86/events/amd/uncore.c
> +++ b/arch/x86/events/amd/uncore.c
> @@ -39,11 +39,11 @@ static int pmu_version;
>  struct amd_uncore_ctx {
>         int refcnt;
>         int cpu;
> -       struct perf_event **events;
>         unsigned long active_mask[BITS_TO_LONGS(NUM_COUNTERS_MAX)];
>         int nr_active;
>         struct hrtimer hrtimer;
>         u64 hrtimer_duration;
> +       struct perf_event *events[];

As the number of counters is fixed and events doesn't grow, this makes
sense to me. Dapeng, what do you think?

Thanks,
Ian

>  };
>
>  struct amd_uncore_pmu {
> @@ -488,10 +488,8 @@ static void amd_uncore_ctx_free(struct amd_uncore *uncore, unsigned int cpu)
>                 if (cpu == ctx->cpu)
>                         cpumask_clear_cpu(cpu, &pmu->active_mask);
>
> -               if (!--ctx->refcnt) {
> -                       kfree(ctx->events);
> +               if (!--ctx->refcnt)
>                         kfree(ctx);
> -               }
>
>                 *per_cpu_ptr(pmu->ctx, cpu) = NULL;
>         }
> @@ -536,18 +534,11 @@ static int amd_uncore_ctx_init(struct amd_uncore *uncore, unsigned int cpu)
>                 /* Allocate context if sibling does not exist */
>                 if (!curr) {
>                         node = cpu_to_node(cpu);
> -                       curr = kzalloc_node(sizeof(*curr), GFP_KERNEL, node);
> +                       curr = kzalloc_node(struct_size(curr, events, pmu->num_counters), GFP_KERNEL, node);
>                         if (!curr)
>                                 goto fail;
>
>                         curr->cpu = cpu;
> -                       curr->events = kzalloc_node(sizeof(*curr->events) *
> -                                                   pmu->num_counters,
> -                                                   GFP_KERNEL, node);
> -                       if (!curr->events) {
> -                               kfree(curr);
> -                               goto fail;
> -                       }
>
>                         amd_uncore_init_hrtimer(curr);
>                         curr->hrtimer_duration = (u64)update_interval * NSEC_PER_MSEC;
> --
> 2.54.0
>