[Nouveau] [Bug 96355] New: Performance: extra&costly SSBO validation even when SSBO aren't used

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=96355

            Bug ID: 96355
           Summary: Performance: extra&costly SSBO validation even when
                    SSBO aren't used
           Product: Mesa
           Version: git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/DRI/nouveau
          Assignee: nouveau at lists.freedesktop.org
          Reporter: gregory.hainaut at gmail.com
        QA Contact: nouveau at lists.freedesktop.org

Hello,

I'm currently trying to profile my application (PCSX2) with Mesa. I don't know
if my GPU (GTX760) is properly reclocked but my app is often CPU limited. It
could just be the IO operation that are very slow.

Anyway, Perf-Event shows that nvc0_validate_buffers is (too) often called.
+    8.78%     7.98%  pcsx2_GSReplayL  nouveau_dri.so  nvc0_validate_buffers

My understanding of the code is that every time we switch a shader program, a
full SSBO bind/validation is called. nvc0_set_shader_buffers will dirty buffer
state (NVC0_NEW_3D_BUFFERS). The trick is that my application doesn't use SSBO
(only UBO). Is it expected to call SSBO validation code when the shader program
doesn't use them? If not, a validation shortcut will be nice.

If it can help, here the backtrace from nvc0_set_shader_buffers 

#0  nvc0_set_shader_buffers (pipe=0x87c51e0, shader=0, start=16, nr=16,
buffers=0x0) at nvc0/nvc0_state.c:1331
#1  0xf464acc4 in st_bind_ssbos (shader=0x8b106bc, shader_type=0, st=0x877ca38,
st=0x877ca38) at state_tracker/st_atom_storagebuf.c:86
#2  0xf464ad0d in bind_vs_ssbos (st=0x877ca38) at
state_tracker/st_atom_storagebuf.c:101
#3  0xf4647411 in st_validate_state (st=0x877ca38, pipeline=ST_PIPELINE_RENDER)
at state_tracker/st_atom.c:289
#4  0xf46638ef in st_draw_vbo (ctx=0x8801f60, prims=0xffffa990, nr_prims=1,
ib=0xffffa980, index_bounds_valid=0 '\000', min_index=4294967295,
max_index=4294967295, tfb_vertcount=0x0, 
    stream=0, indirect=0x0) at state_tracker/st_draw.c:176
#5  0xf46270f9 in vbo_validated_drawrangeelements (ctx=ctx at entry=0x8801f60,
mode=mode at entry=4, index_bounds_valid=0 '\000', start=4294967295,
end=4294967295, count=6, type=5125, 
    indices=0x25258, basevertex=19047, numInstances=1, baseInstance=0) at
vbo/vbo_exec_array.c:849
#6  0xf46274bc in vbo_exec_DrawElementsBaseVertex (mode=4, count=6, type=5125,
indices=0x25258, basevertex=19047) at vbo/vbo_exec_array.c:1007
#7  0xf6ddf422 in shared_dispatch_stub_702 (mode=4, count=6, type=5125,
indices=0x25258, basevertex=19047) at shared-glapi/glapi_mapi_tmp.h:21235
#8  0xf6362e0a in Draw (this=<optimized out>, this=<optimized out>,
basevertex=<optimized out>, mode=<optimized out>)

Feel free to ask trace/debug info.

Best regards

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