Commit 991bfc64 authored May 17, 2017 by Chris Wilson

drm/i915: Make ptr_unpack_bits() more function-like



ptr_unpack_bits() is a function-like macro, as such it is meant to be
replaceable by a function. In this case, we should be passing in the
out-param as a pointer.

Bizarrely this does affect code generation:

function                                     old     new   delta
i915_gem_object_pin_map                      409     389     -20

An improvement(?) in this case, but one can't help wonder what
strict-aliasing optimisations we are preventing.

The generated code looks identical in using ptr_unpack_bits (no extra
motions to stack, the pointer and bits appear to be kept in registers),
the difference appears to be code ordering and with a reorder it is able
to use smaller forward jumps.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170517121007.27224-3-chris@chris-wilson.co.uk

parent 47624cc3

drivers/gpu/drm/i915/i915_gem.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -2612,7 +2612,7 @@ void i915_gem_object_pin_map(struct drm_i915_gem_object obj,
		}
		GEM_BUG_ON(!obj->mm.pages);

		ptr = ptr_unpack_bits(obj->mm.mapping, has_type);
		ptr = ptr_unpack_bits(obj->mm.mapping, &has_type);
		if (ptr && has_type != type) {
		if (pinned) {
		ret = -EBUSY;

drivers/gpu/drm/i915/i915_utils.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -77,7 +77,7 @@

		#define ptr_unpack_bits(ptr, bits) ({ \
		unsigned long __v = (unsigned long)(ptr); \
		(bits) = __v & ~PAGE_MASK; \
		*(bits) = __v & ~PAGE_MASK; \
		(typeof(ptr))(__v & PAGE_MASK); \
		})