[Mesa-dev] [PATCH] i965/gen7: always lower textureGrad() on gen7
Chia-I Wu
olvaffe at gmail.com
Mon Sep 9 22:07:27 PDT 2013
On Tue, Sep 10, 2013 at 3:48 AM, Ian Romanick <idr at freedesktop.org> wrote:
> On 09/05/2013 08:57 AM, Chia-I Wu 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.
>>
>> 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.
>
> Any results? Still waiting...
There is no difference in image quality as far as I can tell. Here
are the screenshots of every 100 frames before and after the change
https://www.dropbox.com/s/mdqh0e42sf0xfro/compare-textureGrad-lowering.tar.gz
(297MB)
They are taken with the game's built-in mechanism and effects such as
bullets or explosions are off a bit between runs.
>>> -- 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
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