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drm/i915: optimise i915_gem_object_map() for small objects

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We're using this function for ringbuffers and other "small" objects, so
it's worth avoiding an extra malloc()/free() cycle if the page array is
small enough to put on the stack. Here we've chosen an arbitrary cutoff
of 32 (4k) pages, which is big enough for a ringbuffer (4 pages) or a
context image (currently up to 22 pages).

v5:
    change name of local array [Chris Wilson]

Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1463741647-15666-3-git-send-email-chris@chris-wilson.co.uk
This commit is contained in:
Dave Gordon 2016-05-20 11:54:05 +01:00 committed by Chris Wilson
parent dd6034c67a
commit b338fa473e
1 changed files with 10 additions and 5 deletions
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15
drivers/gpu/drm/i915/i915_gem.c
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@ -2404,7 +2404,8 @@ static void *i915_gem_object_map(const struct drm_i915_gem_object *obj)
unsigned long n_pages = obj->base.size >> PAGE_SHIFT;
struct sg_table *sgt = obj->pages;
struct sg_page_iter sg_iter;
struct page **pages;
struct page *stack_pages[32];
struct page **pages = stack_pages;
unsigned long i = 0;
void *addr;
@ -2412,9 +2413,12 @@ static void *i915_gem_object_map(const struct drm_i915_gem_object *obj)
if (n_pages == 1)
return kmap(sg_page(sgt->sgl));
pages = drm_malloc_gfp(n_pages, sizeof(*pages), GFP_TEMPORARY);
if (!pages)
return NULL;
if (n_pages > ARRAY_SIZE(stack_pages)) {
/* Too big for stack -- allocate temporary array instead */
pages = drm_malloc_gfp(n_pages, sizeof(*pages), GFP_TEMPORARY);
if (!pages)
return NULL;
}
for_each_sg_page(sgt->sgl, &sg_iter, sgt->nents, 0)
pages[i++] = sg_page_iter_page(&sg_iter);
@ -2424,7 +2428,8 @@ static void *i915_gem_object_map(const struct drm_i915_gem_object *obj)
addr = vmap(pages, n_pages, 0, PAGE_KERNEL);
drm_free_large(pages);
if (pages != stack_pages)
drm_free_large(pages);
return addr;
}