[Bug 98455] UnrealEngine v4 demos startup (CS compilation) never finishes

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Wed Oct 26 16:49:50 UTC 2016 

https://bugs.freedesktop.org/show_bug.cgi?id=98455

            Bug ID: 98455
           Summary: UnrealEngine v4 demos startup (CS compilation) never
                    finishes
           Product: Mesa
           Version: git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/DRI/i965
          Assignee: idr at freedesktop.org
          Reporter: eero.t.tamminen at intel.com
        QA Contact: intel-3d-bugs at lists.freedesktop.org

Created attachment 127553
  --> https://bugs.freedesktop.org/attachment.cgi?id=127553&action=edit
MESA_GLSL=dump INTEL_DEBUG=perf,cs,vs,fs,hs,ds output

Mesa 12.0 and latest Mesa from git (aca491341b57fac05901943d693e264b589925f5)
never finish compiling Subway Reflections and Effects Cave demos compute
shaders.

This is where it stops progressing:
-----------
$ INTEL_DEBUG=perf Engine/Binaries/Linux/Effects
...
SIMD16 shader failed to compile: FS compile failed: Failure to register
allocate.  Reduce number of live scalar values to avoid this.
Multi-LOD fast clear - giving up (512x256x7).
Multi-LOD fast clear - giving up (512x256x7).
VS compile took 0.430 ms and stalled the GPU
SIMD16 shader failed to compile: FS compile failed: Failure to register
allocate.  Reduce number of live scalar values to avoid this.
Unsupported form of variable indexing in VS; falling back to very inefficient
code generation
Layered fast clear - giving up. (16x1616)
Layered fast clear - giving up. (16x1616)
Recompiling fragment shader for program 274
  number of color buffers 2->1
Multi-LOD fast clear - giving up (128x128x7).
128x57624 miptree too large to blit, falling back to untiledRecompiling
fragment shader for program 127
  number of color buffers 0->5
Recompiling fragment shader for program 284
  number of color buffers 1->0
Recompiling fragment shader for program 286
  number of color buffers 1->0
SIMD16 shader failed to compile: FS compile failed: Failure to register
allocate.  Reduce number of live scalar values to avoid this.
Unsupported form of variable indexing in CS; falling back to very inefficient
code generation
compute shader triggered register spilling.  Try reducing the number of live
scalar values to improve performance.
-----------

I waited until next day without Mesa outputting anything more and demo not
starting.  According to perf, Mesa is still compiling shaders.  At that point,
demo memory usage had grown from 2GB to 10GB.

If I use MESA_GL_VERSION_OVERRIDE=4.2 to disable compute shader use, demos
start in <10 seconds and use <2GB memory.


According to perf, after 20 hours of compiling, this is where Mesa spends its
time (within one 5 minute period):
-----------------------------------------------------
33,23%  RenderThread  i965_dri.so  ra_allocate
20,88%  RenderThread  i965_dri.so  fs_visitor::virtual_grf_interferes
17,70%  RenderThread  i965_dri.so  ra_add_node_adjacency
 9,44%  RenderThread  i965_dri.so  fs_visitor::assign_regs
 5,51%  RenderThread  i965_dri.so  brw::fs_live_variables::compute_start_end
 2,94%  RenderThread  i965_dri.so  decrement_q.isra.2
 2,06%  RenderThread  i965_dri.so  ra_add_node_interference
 1,08%  RenderThread  i965_dri.so 
brw::fs_live_variables::compute_live_variables
-----------------------------------------------------

According to Martin, he cannot reproduce the issue on Arch Linux, so it's
possible that it's some bug in code that manifests only with certain build /
run-time environment.

However, it happens both with Mesa compiled on up to date Ubuntu 16.04, also
when using GCC 4.9 instead of the default GCC 5.4.  It happens also another
machine, when using latest drm-intel kernel and X instead of Ubuntu versions of
them.

Attached is the 40MB shader code output from Mesa until that point.  Just
search for the last "falling back to very inefficient code generation" message
to see what Mesa is trying to compile.


Not sure whether it's related, but before the issue, there are several Valgrind
warnings about shader compilation accessing already freed memory (in some
earlier compiled shaders), like this:
--------------------------------
==16996== Thread 9 RenderThread 1:
==16996== Invalid read of size 1
==16996==    at 0x4C30F62: strlen (in
/usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==16996==    by 0xEA94D16: ralloc_strdup (ralloc.c:350)
==16996==    by 0xEAD1104: nir_shader_clone (nir_clone.c:714)
==16996==    by 0xEBC0D00: brw_compile_fs (brw_fs.cpp:6422)
==16996==    by 0xEB641FD: brw_codegen_wm_prog (brw_wm.c:147)
==16996==    by 0xEB64D34: brw_upload_wm_prog (brw_wm.c:587)
==16996==    by 0xEB5CC02: brw_upload_programs (brw_state_upload.c:736)
==16996==    by 0xEB5CC02: brw_upload_pipeline_state (brw_state_upload.c:835)
==16996==    by 0xEB5CC02: brw_upload_render_state (brw_state_upload.c:896)
==16996==    by 0xEB459B9: brw_try_draw_prims (brw_draw.c:584)
==16996==    by 0xEB459B9: brw_draw_prims (brw_draw.c:675)
==16996==    by 0xE9730AF: vbo_validated_drawrangeelements
(vbo_exec_array.c:813)
==16996==    by 0xE97314A: vbo_exec_DrawElementsInstanced
(vbo_exec_array.c:989)
==16996==    at 0x4C2EDEB: free (in
/usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==16996==    by 0xEA9490C: unsafe_free (ralloc.c:251)
==16996==    by 0xEA9490C: unsafe_free (ralloc.c:251)
==16996==    by 0xEB642B9: brw_codegen_wm_prog (brw_wm.c:189)
==16996==    by 0xEB64E66: brw_fs_precompile (brw_wm.c:647)
==16996==    by 0xEB4CE36: brw_shader_precompile (brw_link.cpp:53)
==16996==    by 0xEB4CE36: brw_link_shader (brw_link.cpp:289)
==16996==    by 0xE9F95A1: _mesa_glsl_link_shader (ir_to_mesa.cpp:3067)
==16996==  Block was alloc'd at
==16996==    at 0x4C2FB55: calloc (in
/usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==16996==    by 0xEA94A41: rzalloc_size (ralloc.c:125)
==16996==    by 0xEA94D24: ralloc_size (ralloc.c:119)
==16996==    by 0xEA94D24: ralloc_array_size (ralloc.c:190)
==16996==    by 0xEA94D24: ralloc_strdup (ralloc.c:351)
==16996==    by 0xEAD1104: nir_shader_clone (nir_clone.c:714)
==16996==    by 0xEBC0D00: brw_compile_fs (brw_fs.cpp:6422)
==16996==    by 0xEB641FD: brw_codegen_wm_prog (brw_wm.c:147)
==16996==    by 0xEB64E66: brw_fs_precompile (brw_wm.c:647)
==16996==    by 0xEB4CE36: brw_shader_precompile (brw_link.cpp:53)
==16996==    by 0xEB4CE36: brw_link_shader (brw_link.cpp:289)
==16996==    by 0xE9F95A1: _mesa_glsl_link_shader (ir_to_mesa.cpp:3067)
--------------------------------

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