[Intel-gfx] [PATCH 1/2] drm/i915: refactor i915_gem_object_pin_map()

[Chris Wilson]

On Tue, Apr 19, 2016 at 06:40:07PM +0100, Dave Gordon wrote:
> From: Alex Dai <yu.dai at intel.com>
> 
> The recently-added i915_gem_object_pin_map() can be further optimised
> for "small" objects. To facilitate this, and simplify the error paths
> before adding the new code, this patch pulls out the "mapping" part of
> the operation (involving local allocations which must be undone before
> return) into its own subfunction.
> 
> The next patch will then insert the new optimisation into the middle of
> the now-separated subfunction.
> 
> This reorganisation will probably not affect the generated code, as the
> compiler will most likely inline it anyway, but it makes the logical
> structure a bit clearer and easier to modify.
> 
> Signed-off-by: Dave Gordon <david.s.gordon at intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 61 +++++++++++++++++++++++++++--------------
>  1 file changed, 40 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 6ce2c31..fc42be0 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -2396,6 +2396,45 @@ static void i915_gem_object_free_mmap_offset(struct drm_i915_gem_object *obj)
>  	return 0;
>  }
>  
> +/* The 'mapping' part of i915_gem_object_pin_map() below */
> +static void *i915_gem_object_map(const struct drm_i915_gem_object *obj)
> +{
> +	unsigned long n_pages = obj->base.size >> PAGE_SHIFT;
> +	struct scatterlist *sg = obj->pages->sgl;
> +	struct sg_page_iter sg_iter;
> +	struct page **pages;
> +	unsigned long i = 0;
> +	void *addr = NULL;
> +
> +	/* A single page can always be kmapped */
> +	if (n_pages == 1)
> +		return kmap(sg_page(sg));
> +
> +	pages = drm_malloc_gfp(n_pages, sizeof(*pages), GFP_TEMPORARY);
> +	if (pages == NULL) {
> +		DRM_DEBUG_DRIVER("Failed to get space for pages\n");
> +		return NULL;
> +	}
> +
> +	for_each_sg_page(sg, &sg_iter, n_pages, 0) {
> +		pages[i] = sg_page_iter_page(&sg_iter);

Just pages[i++] = sg_page_iter_page(&sg_iter);

> +		if (++i == n_pages) {
> +			addr = vmap(pages, n_pages, 0, PAGE_KERNEL);
> +			break;
> +		}
> +	}
> +
> +	/* We should have got here via the 'break' above */
> +	WARN_ON(i != n_pages);
> +	if (addr == NULL)
> +		DRM_DEBUG_DRIVER("Failed to vmap pages\n");

As this is a very, very confused loop.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre