[PATCH] input: calloc minimization for xi2mask_new

[Jasper St. Pierre]

Though I'd love to look into the gnome-shell issue more (changing to the
overview should not call XIGrabKey/XIUngrabKey a ton of times), the
handling in the server here was ridiculous and this is obviously an
improvement.

Reviewed-by: Jasper St. Pierre <jstpierre at mecheye.net>



On Tue, Sep 10, 2013 at 2:18 PM, Adam Jackson <ajax at redhat.com> wrote:

> There's no reason to do this as (nmasks + 2) callocs, and it's a
> surprisingly hot path.  Turns out you hit this ~once per passive grab,
> and you do a few bajillion passive grab changes every time you enter or
> leave the overview in gnome-shell.  According to a callgrind of Xorg
> with gnome-shell-perf-tool run against it:
>
> Ir before: 721437275
> Ir after:  454227086
>
> Signed-off-by: Adam Jackson <ajax at redhat.com>
> ---
>  dix/inpututils.c | 30 +++++++++++++-----------------
>  1 file changed, 13 insertions(+), 17 deletions(-)
>
> diff --git a/dix/inpututils.c b/dix/inpututils.c
> index 9e38e17..a10a7c7 100644
> --- a/dix/inpututils.c
> +++ b/dix/inpututils.c
> @@ -960,8 +960,15 @@ XI2Mask *
>  xi2mask_new_with_size(size_t nmasks, size_t size)
>  {
>      int i;
> +    int alloc_size;
> +    unsigned char *cursor;
> +    XI2Mask *mask;
>
> -    XI2Mask *mask = calloc(1, sizeof(*mask));
> +    alloc_size = sizeof(struct _XI2Mask)
> +              + nmasks * sizeof(unsigned char *)
> +              + nmasks * size;
> +
> +    mask = calloc(1, alloc_size);
>
>      if (!mask)
>          return NULL;
> @@ -969,20 +976,14 @@ xi2mask_new_with_size(size_t nmasks, size_t size)
>      mask->nmasks = nmasks;
>      mask->mask_size = size;
>
> -    mask->masks = calloc(mask->nmasks, sizeof(*mask->masks));
> -    if (!mask->masks)
> -        goto unwind;
> +    mask->masks = (unsigned char **)(mask + 1);
> +    cursor = (unsigned char *)(mask + 1) + nmasks * sizeof(unsigned char
> *);
>
> -    for (i = 0; i < mask->nmasks; i++) {
> -        mask->masks[i] = calloc(1, mask->mask_size);
> -        if (!mask->masks[i])
> -            goto unwind;
> +    for (i = 0; i < nmasks; i++) {
> +        mask->masks[i] = cursor;
> +       cursor += size;
>      }
>      return mask;
> -
> - unwind:
> -    xi2mask_free(&mask);
> -    return NULL;
>  }
>
>  /**
> @@ -1003,14 +1004,9 @@ xi2mask_new(void)
>  void
>  xi2mask_free(XI2Mask **mask)
>  {
> -    int i;
> -
>      if (!(*mask))
>          return;
>
> -    for (i = 0; (*mask)->masks && i < (*mask)->nmasks; i++)
> -        free((*mask)->masks[i]);
> -    free((*mask)->masks);
>      free((*mask));
>      *mask = NULL;
>  }
> --
> 1.8.3.1
>
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-- 
  Jasper
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