Hi,
On 06/25/2015 03:53 PM, Davin McCall wrote:
On 25/06/15 12:27, Eero Tamminen wrote:
On 06/25/2015 02:48 AM, Davin McCall wrote:
In terms of performance:
(export LIBGL_ALWAYS_SOFTWARE=1; time glmark2)
For Intel driver, INTEL_NO_HW=1 could be used.
(Do other drivers have something similar?)
Unfortunately I do not have an Intel display set up.
If you can get libINTEL_DEVID_OVERRIDEdrm to use libdrm_intel, you can
fake desired
InteL HW to Mesa with INTEL_DEVID_OVERRIDE environment variable.
Similarly to INTEL_NO_HW, it prevents batches from being submitted
to GPU.
What exactly would INTEL_NO_HW=1 do?
http://www.mesa3d.org/envvars.html
"INTEL_NO_HW - if set to 1, prevents batches from being submitted to the
hardware."
I.e. driver does only CPU / user-space side things and skips GPU /
kernel side work.
Again, only a very small improvement when strict aliasing is enabled.
With the above in mind it is reasonable to question whether this patch
is worthwhile.
IMHO to evaluate that, we would need data for more drivers, not just
for SW rendering.
Given that we are talking about using a compiler option when compiling
Mesa itself, I do not imagine that we would see a more significant
change in performance when using HW assisted rendering. The code that
runs on the GPU is the same in either case.
When testing 3D driver CPU side optimizations, one should either use
test specifically written for testing driver CPU overhead (proprietary
benchmarks have such tests) or force test-case to be CPU bound e.g. with
INTEL_NO_HW.
Using the R600 driver (and Radeon 6770 hardware) I get:
With -fno-strict-aliasing:
glmark2 Score: 1614
real 5m31.729s
user 0m43.828s
sys 0m20.892s
With strict aliasing:
glmark2 Score: 1626
real 5m31.725s
user 0m43.496s
sys 0m20.924s
This is all on x86, 32-bit. It's possible that more of an improvement
would be seen on less register-starved architectures (including Intel
x86-64), since more register spills/loads can potentially be avoided. I
don't have the capability to test that right now. It's entirely possible
that compiling without -fno-strict-aliasing on x86-64 will not (at
present, even with this patch applied) produce a working library.
- Eero
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