Bug 90258 - [IVB] spec.glsl-1_10.execution.fs-dfdy-accuracy fails intermittently
Summary: [IVB] spec.glsl-1_10.execution.fs-dfdy-accuracy fails intermittently
Alias: None
Product: Mesa
Classification: Unclassified
Component: Drivers/DRI/i965 (show other bugs)
Version: git
Hardware: x86-64 (AMD64) Linux (All)
: medium normal
Assignee: Tapani Pälli
QA Contact: Intel 3D Bugs Mailing List
Depends on:
Reported: 2015-04-30 16:34 UTC by Mark Janes
Modified: 2015-05-13 06:11 UTC (History)
2 users (show)

See Also:
i915 platform:
i915 features:

patch to fix the issue (1.42 KB, patch)
2015-05-12 11:20 UTC, Tapani Pälli
Details | Splinter Review

Description Mark Janes 2015-04-30 16:34:15 UTC
The jenkins regression system began reproducing IVB failures for this piglit test somewhere after 10.5.  On the CI system it reproduces fairly regularly (10% of the time?).

The test passes all other platforms, and does not reproduce (yet) in the 10.5 branch.

Test Output:
/tmp/build_root/m64/lib/piglit/bin/shader_runner /tmp/build_root/m64/lib/piglit/tests/spec/glsl-1.10/execution/fs-dfdy-accuracy.shader_test -auto
Probe color at (36,164)
  Expected: 0.000000 1.000000 0.000000 1.000000
  Observed: 1.000000 0.000000 0.000000 1.000000
Comment 1 Tapani Pälli 2015-05-12 09:44:01 UTC
This happens quite reliably when running a while loop in bash, I've bisected this to following commit:

--- 8< -----------------------------------
dd5c8250537640f92dbc1ee63d516c6e3e2aaf77 is the first bad commit
commit dd5c8250537640f92dbc1ee63d516c6e3e2aaf77
Author: Matt Turner <mattst88@gmail.com>
Date:   Tue Apr 14 12:40:34 2015 -0700

    i965: Replace guess_execution_size with something simpler.
    guess_execution_size() does two things:
       1. Cope with small destination registers.
       2. Cope with SIMD8 vs SIMD16 mode.
    This patch replaces the first with a simple if block in brw_set_dest: if
    the destination register width is less than 8, you probably want the
    execution size to match.  (I didn't put this in the 3src block because
    it doesn't seem to matter.)
    Since only the FS compiler cares about SIMD16 mode, it's easy to just
    set the default execution size there.
    This pattern was already been proven in the Gen8+ generator, but we
    didn't port it back to the existing generator when we combined the two.
    This is based on a patch from Ken from about a year ago. I've rebased it
    and and fixed a few bugs.
    Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>
Comment 2 Tapani Pälli 2015-05-12 10:20:55 UTC
Between passing and a failing run there is no difference in the generated assembly, I checked this by comparing INTEL_DEBUG=vs,fs outputs.
Comment 3 Tapani Pälli 2015-05-12 11:01:30 UTC
However with patch and before it there are changes in assembly:


add(8)          g7<1>F          g5<4,4,1>.xyxyF -g5<4,4,1>.zwzwF { align16 1Q };
add(8)          g8<1>F          g6<4,4,1>.xyxyF -g6<4,4,1>.zwzwF { align16 2Q };


add(16)         g7<1>F          g5<4,4,1>.xyxyF -g5<4,4,1>.zwzwF { align16 1H };
add(16)         g8<1>F          g6<4,4,1>.xyxyF -g6<4,4,1>.zwzwF { align16 1H };

with help from Curro I think I can tackle this one!
Comment 4 Tapani Pälli 2015-05-12 11:20:56 UTC
Created attachment 115712 [details] [review]
patch to fix the issue

will test
Comment 5 Tapani Pälli 2015-05-13 06:11:47 UTC
pushed to master

(sorry Mark, I forgot to add tested-by tag, many thanks for testing!)

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