On 13/12/2016 12:41, Chris Wilson wrote:
On Tue, Dec 13, 2016 at 12:22:18PM +0000, Tvrtko Ursulin wrote:From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx> A few details to hopefully make a very hot function a tiny bit more efficient: 1. Cast VM pointers before substraction to save the compiler doing a smart one which includes multiplication.Indeed. Not pretty though. static always_inline __kernel_ptrdiff_t ptrdiff(const void *a, const void *b) { return a - b; } cmp = ptrdiff(vma->vm, vm); if (cmp) return cmp;
Pffifle as you would say. :)
2. Use smaller type for comparison since we only care about the sign.Should be a no-op since the compiler also should only care about the sign and not be moving the registers about, just the cc and we should be inlining... Is gcc not smart enough? :(
I am pretty sure there was a significant difference in the size of generated code so apparently it isn't.
3. Prefer the ppgtt lookup branch and inline it, allowing the compiler to optimise out the second part of i915_vma_compare and save one call indirection.This runs counter to a better optimisation that completely avoids calling obj_to_vma for ppgtt lookups (i.e. in execbuffer we go straight from handle to vma, skipping the handle to obj intermediate lookup). Primary caller for this function should be ggtt users, with single negative lookups before creating the ppgtt vma.
Empirically ppgtt users call this much much more on any benchmarks I've tried since with the change all I see is lookup_and_create in the profiles and not obj_to_vma.
Regards, Tvrtko _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
