[Intel-gfx] [PATCH 13/14] drm/i915: Use binary search when looking for shadowed registers

[Chris Wilson]

On Fri, Sep 30, 2016 at 06:48:48PM +0100, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> Simply replace the linear search with the kernel's binary
> search implementation. There is only six registers currently
> in that table so this may not be that interesting. It adds a
> function call so hopefully remains performance neutral for now.
> 
> v2: No need for manual conversion to bool for return.
>     (Joonas Lahtinen)
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Reviewed-by: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> ---
>  drivers/gpu/drm/i915/intel_uncore.c | 26 +++++++++++++++++++++-----
>  1 file changed, 21 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index 10b21516a7de..70a7fef79846 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -689,14 +689,30 @@ static void intel_shadow_table_check(void)
>  #endif
>  }
>  
> +static int mmio_reg_cmp(const void *key, const void *elt)
> +{
> +	u32 offset = (u32)(unsigned long)key;
> +	i915_reg_t *reg = (i915_reg_t *)elt;
> +
> +	if (offset < i915_mmio_reg_offset(*reg))
> +		return -1;
> +	else if (offset > i915_mmio_reg_offset(*reg))
> +		return 1;
> +	else
> +		return 0;

There's no issue with using

	return offset - i915_mmio_reg_offset(*reg)

here.

> +}
> +
>  static bool is_gen8_shadowed(u32 offset)
>  {
> -	int i;
> -	for (i = 0; i < ARRAY_SIZE(gen8_shadowed_regs); i++)
> -		if (offset == gen8_shadowed_regs[i].reg)
> -			return true;
> +	i915_reg_t *reg;
>  
> -	return false;
> +	reg = bsearch((void *)(unsigned long)offset,
> +		      (const void *)gen8_shadowed_regs,
> +		      ARRAY_SIZE(gen8_shadowed_regs),
> +		      sizeof(i915_reg_t),
> +		      mmio_reg_cmp);
> +
> +	return reg;

Or just return bseearch() ? (Probably like this for easing future
patches.)
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre