[Mesa-dev] [PATCH] i965/gen7: always lower textureGrad() on gen7
Chia-I Wu
olvaffe at gmail.com
Fri Sep 6 03:05:22 PDT 2013
On Thu, Sep 5, 2013 at 9:57 PM, Chia-I Wu <olvaffe at gmail.com> wrote:
> On Thu, Sep 5, 2013 at 5:12 PM, Chris Forbes <chrisf at ijw.co.nz> wrote:
>> A possible explanation for the perf change is that Xonotic uses
>> anisotropic filtering at this quality level. Lowering to txl defeats
>> it.
> I had a look at that. gl_sampler->MaxAnisotropy is never greater than
> 1.0 in gen7_update_sampler_state() so there is no anisotropic
> filtering in this case.
>
> It makes sense to me that avoiding punting to SIMD8 helps the
> performance. But it is not clear to me why >10% performance change
> can still be observed when INTEL_DEBUG=no16 is specified. A
> reasonable explanation is that the image quality is degraded in some
> way, which is why I am still nervous about the change.
With INTEL_DEBUG=no16 set, the same trick hurts the performance on
Haswell by about 5%. That is, sample_d on Haswell is faster than the
one emulated with sample_l.
But since the trick makes SIMD16 possible, it gains 5% more fps when
INTEL_DEBUG=no16 is not set.
> An alternative approach to avoid punting seems to emulate SIMD16
> sample_d with two SIMD8 sample_d. It will take longer to implement
> given my familiarity with the code, and may be less performant. BUt
> that would allow things like anisotropic filtering to be honored.
>
>
>> It would be worth doing an image quality comparison before and after the change.
> Yeah, that is worth doing. I will do that.
>
>>
>> -- Chris
>>
>> On Thu, Sep 5, 2013 at 8:35 PM, Chia-I Wu <olvaffe at gmail.com> wrote:
>>> sample_d is slower than the lowered version on gen7. For gen7, this improves
>>> Xonotic benchmark with Ultimate effects by as much as 25%:
>>>
>>> before the change: 40.06 fps
>>> after the change: 51.10 fps
>>> after the change with INTEL_DEBUG=no16: 44.46 fps
>>>
>>> As sample_d is not allowed in SIMD16 mode, I firstly thought the difference
>>> was from SIMD8 versus SIMD16. If that was the case, we would want to apply
>>> brw_lower_texture_gradients() only on fragment shaders in SIMD16 mode.
>>>
>>> But, as the numbers show, there is still 10% improvement when SIMD16 is forced
>>> off after the change. Thus textureGrad() is lowered unconditionally for now.
>>> Due to this and that I haven't tried it on Haswell, this is still RFC.
>>>
>>> No piglit regressions.
>>>
>>> Signed-off-by: Chia-I Wu <olvaffe at gmail.com>
>>> ---
>>> .../dri/i965/brw_lower_texture_gradients.cpp | 54 ++++++++++++++--------
>>> 1 file changed, 36 insertions(+), 18 deletions(-)
>>>
>>> diff --git a/src/mesa/drivers/dri/i965/brw_lower_texture_gradients.cpp b/src/mesa/drivers/dri/i965/brw_lower_texture_gradients.cpp
>>> index 1589a20..f3fcb56 100644
>>> --- a/src/mesa/drivers/dri/i965/brw_lower_texture_gradients.cpp
>>> +++ b/src/mesa/drivers/dri/i965/brw_lower_texture_gradients.cpp
>>> @@ -34,8 +34,8 @@ using namespace ir_builder;
>>>
>>> class lower_texture_grad_visitor : public ir_hierarchical_visitor {
>>> public:
>>> - lower_texture_grad_visitor(bool has_sample_d_c)
>>> - : has_sample_d_c(has_sample_d_c)
>>> + lower_texture_grad_visitor(bool has_sample_d, bool has_sample_d_c)
>>> + : has_sample_d(has_sample_d), has_sample_d_c(has_sample_d_c)
>>> {
>>> progress = false;
>>> }
>>> @@ -44,6 +44,7 @@ public:
>>>
>>>
>>> bool progress;
>>> + bool has_sample_d;
>>> bool has_sample_d_c;
>>>
>>> private:
>>> @@ -90,22 +91,33 @@ txs_type(const glsl_type *type)
>>> ir_visitor_status
>>> lower_texture_grad_visitor::visit_leave(ir_texture *ir)
>>> {
>>> - /* Only lower textureGrad with shadow samplers */
>>> - if (ir->op != ir_txd || !ir->shadow_comparitor)
>>> + if (ir->op != ir_txd)
>>> return visit_continue;
>>>
>>> - /* Lower textureGrad() with samplerCubeShadow even if we have the sample_d_c
>>> - * message. GLSL provides gradients for the 'r' coordinate. Unfortunately:
>>> - *
>>> - * From the Ivybridge PRM, Volume 4, Part 1, sample_d message description:
>>> - * "The r coordinate contains the faceid, and the r gradients are ignored
>>> - * by hardware."
>>> - *
>>> - * We likely need to do a similar treatment for samplerCube and
>>> - * samplerCubeArray, but we have insufficient testing for that at the moment.
>>> - */
>>> - bool need_lowering = !has_sample_d_c ||
>>> - ir->sampler->type->sampler_dimensionality == GLSL_SAMPLER_DIM_CUBE;
>>> + bool need_lowering = false;
>>> +
>>> + if (ir->shadow_comparitor) {
>>> + /* Lower textureGrad() with samplerCubeShadow even if we have the
>>> + * sample_d_c message. GLSL provides gradients for the 'r' coordinate.
>>> + * Unfortunately:
>>> + *
>>> + * From the Ivybridge PRM, Volume 4, Part 1, sample_d message
>>> + * description: "The r coordinate contains the faceid, and the r
>>> + * gradients are ignored by hardware."
>>> + */
>>> + if (ir->sampler->type->sampler_dimensionality == GLSL_SAMPLER_DIM_CUBE)
>>> + need_lowering = true;
>>> + else if (!has_sample_d_c)
>>> + need_lowering = true;
>>> + }
>>> + else {
>>> + /* We likely need to do a similar treatment for samplerCube and
>>> + * samplerCubeArray, but we have insufficient testing for that at the
>>> + * moment.
>>> + */
>>> + if (!has_sample_d)
>>> + need_lowering = true;
>>> + }
>>>
>>> if (!need_lowering)
>>> return visit_continue;
>>> @@ -154,7 +166,9 @@ lower_texture_grad_visitor::visit_leave(ir_texture *ir)
>>> expr(ir_unop_sqrt, dot(dPdy, dPdy)));
>>> }
>>>
>>> - /* lambda_base = log2(rho). We're ignoring GL state biases for now. */
>>> + /* lambda_base = log2(rho). It will be biased and clamped by values
>>> + * defined in SAMPLER_STATE to get the final lambda.
>>> + */
>>> ir->op = ir_txl;
>>> ir->lod_info.lod = expr(ir_unop_log2, rho);
>>>
>>> @@ -168,8 +182,12 @@ bool
>>> brw_lower_texture_gradients(struct brw_context *brw,
>>> struct exec_list *instructions)
>>> {
>>> + /* sample_d is slower than the lowered version on gen7, and is not allowed
>>> + * in SIMD16 mode. Treating it as unsupported improves the performance.
>>> + */
>>> + bool has_sample_d = brw->gen != 7;
>>> bool has_sample_d_c = brw->gen >= 8 || brw->is_haswell;
>>> - lower_texture_grad_visitor v(has_sample_d_c);
>>> + lower_texture_grad_visitor v(has_sample_d, has_sample_d_c);
>>>
>>> visit_list_elements(&v, instructions);
>>>
>>> --
>>> 1.8.3.1
>>>
>>> _______________________________________________
>>> mesa-dev mailing list
>>> mesa-dev at lists.freedesktop.org
>>> http://lists.freedesktop.org/mailman/listinfo/mesa-dev
>
>
>
> --
> olv at LunarG.com
--
olv at LunarG.com
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