linux-kernel - Re: [rfc, PATCH v1 1/1] min_heap: Make use of cmp_func_t and swap_func

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Message-ID: <CAP-5=fUn9wrgz13HHxq=BDBoOVXHfR-MT-xt5zLmy74oWhQONw@mail.gmail.com>
Date:   Thu, 17 Aug 2023 10:51:04 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [rfc, PATCH v1 1/1] min_heap: Make use of cmp_func_t and
 swap_func_t types

On Thu, Aug 17, 2023 at 10:09 AM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> The types.h defines standard types for comparator and swap functions.
> Convert min_heap to use it.
>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
>  include/linux/min_heap.h | 8 ++++----
>  kernel/events/core.c     | 4 ++--
>  lib/test_min_heap.c      | 6 +++---
>  3 files changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/min_heap.h b/include/linux/min_heap.h
> index 44077837385f..14da37caa235 100644
> --- a/include/linux/min_heap.h
> +++ b/include/linux/min_heap.h
> @@ -26,8 +26,8 @@ struct min_heap {
>   */
>  struct min_heap_callbacks {
>         int elem_size;
> -       bool (*less)(const void *lhs, const void *rhs);
> -       void (*swp)(void *lhs, void *rhs);
> +       cmp_func_t less;

This looks wrong. A cmp_func_t will return -1, for less-than, 0 for
equal, +1 for greater-than whilst the less function here is just
providing less-than as true/false. This is done to avoid common
pitfalls around minimum integer.

> +       swap_func_t swp;

Why pass a size argument when we're specifying the swap function to use anyway?

Thanks,
Ian

>  };
>
>  /* Sift the element at pos down the heap. */
> @@ -55,7 +55,7 @@ void min_heapify(struct min_heap *heap, int pos,
>                 }
>                 if (smallest == parent)
>                         break;
> -               func->swp(smallest, parent);
> +               func->swp(smallest, parent, func->elem_size);
>                 if (smallest == left)
>                         pos = (pos * 2) + 1;
>                 else
> @@ -127,7 +127,7 @@ void min_heap_push(struct min_heap *heap, const void *element,
>                 parent = data + ((pos - 1) / 2) * func->elem_size;
>                 if (func->less(parent, child))
>                         break;
> -               func->swp(parent, child);
> +               func->swp(parent, child, func->elem_size);
>         }
>  }
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 4c72a41f11af..fa344b916290 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -3639,7 +3639,7 @@ void __perf_event_task_sched_out(struct task_struct *task,
>         perf_cgroup_switch(next);
>  }
>
> -static bool perf_less_group_idx(const void *l, const void *r)
> +static int perf_less_group_idx(const void *l, const void *r)
>  {
>         const struct perf_event *le = *(const struct perf_event **)l;
>         const struct perf_event *re = *(const struct perf_event **)r;
> @@ -3647,7 +3647,7 @@ static bool perf_less_group_idx(const void *l, const void *r)
>         return le->group_index < re->group_index;
>  }
>
> -static void swap_ptr(void *l, void *r)
> +static void swap_ptr(void *l, void *r, int size)
>  {
>         void **lp = l, **rp = r;
>
> diff --git a/lib/test_min_heap.c b/lib/test_min_heap.c
> index 7b01b4387cfb..63d0b2f6c060 100644
> --- a/lib/test_min_heap.c
> +++ b/lib/test_min_heap.c
> @@ -11,17 +11,17 @@
>  #include <linux/printk.h>
>  #include <linux/random.h>
>
> -static __init bool less_than(const void *lhs, const void *rhs)
> +static __init int less_than(const void *lhs, const void *rhs)
>  {
>         return *(int *)lhs < *(int *)rhs;
>  }
>
> -static __init bool greater_than(const void *lhs, const void *rhs)
> +static __init int greater_than(const void *lhs, const void *rhs)
>  {
>         return *(int *)lhs > *(int *)rhs;
>  }
>
> -static __init void swap_ints(void *lhs, void *rhs)
> +static __init void swap_ints(void *lhs, void *rhs, int size)
>  {
>         int temp = *(int *)lhs;
>
> --
> 2.40.0.1.gaa8946217a0b
>