[Mesa-dev] [PATCH v5 0/3] asynchronous pbo transfer with glthread

[Marek Olšák]

On Thu, Apr 20, 2017 at 6:53 PM, gregory hainaut
<gregory.hainaut at gmail.com> wrote:
> On Thu, 20 Apr 2017 11:57:08 +0200
> Marek Olšák <maraeo at gmail.com> wrote:
>
>> On Thu, Apr 20, 2017 at 10:28 AM, gregory hainaut
>> <gregory.hainaut at gmail.com> wrote:
>> > On Thu, 20 Apr 2017 12:29:11 +0900
>> > Michel Dänzer <michel at daenzer.net> wrote:
>> >
>> >> On 20/04/17 01:54 AM, Gregory Hainaut wrote:
>> >> > Hello,
>> >> >
>> >> > Please find the latest version that include a small fix for hash deletion. I
>> >> > think the series is good now. Please review/ack it.
>> >>
>> >> I'm afraid I have to NACK it. As discussed in the v4 cover letter
>> >> thread, Mesa's glthread cannot make any libX11 API calls.
>> >>
>> >>
>> >
>> > Hello Michel,
>> >
>> > Just to be sure we are on the same line, let's me do a summary.
>> >
>> > PCSX2 does the following bad pattern
>> > 1/ no call to XInitThread
>> > 2/ XGetGeometry to get the size of the surface
>> > 3/ glDrawArray into the default framebuffer 0 (the window, I'm not sure how to call it)
>> >    => which seem to call DRI2GetBuffersWithFormat under the hood. I guess to get the
>> >       associated buffer of the window.
>> >
>> >
>> > So far it was (kind of) working fine because PCSX2 does tons of PBO transfer. So glthread
>> > was mostly synchronous.
>> >
>> > This series removes the (useless) PBO transfer synchronization. So now glthread is really
>> > asynchronous and the above bad pattern crash as expected.
>> >
>> > I didn't add any libX11 API call on the patches. And I don't think we can remvove the DRI stuff.
>> >
>> > Hum, I don't know what will be the impact on the perf but potentially we can force a synchronization
>> > when there is a draw to framebuffer 0.
>>
>> Can you send us the backtrace when DRI2GetBuffersWithFormat is called
>> by glDrawArrays?
>>
>> Marek
>
> Hello Marek, Michel,
>
> Here the full backtrace.
>
> #0  DRI2GetBuffersWithFormat (dpy=0xc6307e48, drawable=104857784, width=0xdef348c0, height=0xdef348c4, attachments=0xdcc15c88, count=1, outCount=0xdcc15c74) at dri2.c:464
> #1  0xf05bac45 in dri2GetBuffersWithFormat (driDrawable=0xdef348a8, width=0xdef348c0, height=0xdef348c4, attachments=0xdcc15c88, count=1, out_count=0xdcc15c74, loaderPrivate=0xdefc6ef0) at dri2_glx.c:894
> #2  0xe3ec3111 in dri2_drawable_get_buffers (count=<synthetic pointer>, atts=0xdef252f8, drawable=0xdefc7b08) at dri2.c:285
> #3  dri2_allocate_textures (ctx=0xdef15928, drawable=0xdefc7b08, statts=0xdef252f8, statts_count=2) at dri2.c:480
> #4  0xe3ebcbb0 in dri_st_framebuffer_validate (stctx=0xdef4ab10, stfbi=0xdefc7b08, statts=0xdef252f8, count=2, out=0xdcc15d78) at dri_drawable.c:83
> #5  0xe3d37afc in st_framebuffer_validate (stfb=stfb at entry=0xdef24f58, st=st at entry=0xdef4ab10) at state_tracker/st_manager.c:189
>     Note "print stfb->Base->Name" give me 0
> #6  0xe3d38649 in st_manager_validate_framebuffers (st=0xdef4ab10) at state_tracker/st_manager.c:869
> #7  0xe3cd0580 in st_validate_state (st=0xdef4ab10, pipeline=ST_PIPELINE_RENDER) at state_tracker/st_atom.c:174
> #8  0xe3cf935d in st_draw_vbo (ctx=0xdef7f8f8, prims=0xdcc15f40, nr_prims=1, ib=0x0, index_bounds_valid=1 '\001', min_index=39911, max_index=39914, tfb_vertcount=0x0, stream=0, indirect=0x0) at state_tracker/st_draw.c:191
> #9  0xe3caf35e in vbo_draw_arrays (baseInstance=0, numInstances=1, count=4, start=39911, mode=5, ctx=0xdef7f8f8) at vbo/vbo_exec_array.c:427
> #10 vbo_exec_DrawArrays (mode=5, start=39911, count=4) at vbo/vbo_exec_array.c:575
> #11 0xe3be4f07 in _mesa_unmarshal_DrawArrays (ctx=0xdef7f8f8, cmd=0xc41574b0) at main/marshal_generated.c:26644
> #12 _mesa_unmarshal_dispatch_cmd (ctx=0xdef7f8f8, cmd=0xc41574b0) at main/marshal_generated.c:42457
> #13 0xe3ba8af0 in glthread_unmarshal_batch (release_batch=true, batch=0xc4157410, ctx=0xdef7f8f8) at main/glthread.c:64
> #14 glthread_worker (data=0xdef7f8f8) at main/glthread.c:110
>
>
>> If this DRI2GetBuffersWithFormat call results in libX11 API calls on the
>> glthread, that's a bug which needs to be fixed, either by moving the
>> DRI2GetBuffersWithFormat call to the main thread or (if possible) by
>> changing DRI2GetBuffersWithFormat to use XCB directly.

First, we need to understand why it's happening. Does the app use the
front buffer? Does it ever call glDrawBuffer(GL_FRONT) or
glReadBuffer(GL_FRONT)?

>
> Ok. On one hand, moving DRI2GetBuffersWithFormat to main thread won't be easy. I think we need to
> keep track of the current bound framebuffer on the app thread. So we can force a sync
> on gl operation that will access the framebuffer 0.
>
> On the other hand, GLX/XLIB/XCB interactions are  quite foggy for me. It seem there already some xcb codes
> in various place typically EGL and the xcb_dri2 extension. So maybe there is a reason that code wasn't ported here.
> In particular, I saw this option in configure
>   --enable-glx[=dri|xlib|gallium-xlib] enable the GLX library and choose an implementation
>               [default=auto]

glx means libGL. dri means libGL loads _dri.so files. xlib means that
libGL itself contains swrast and doesn't load any drivers.
gallium-xlib means that libGL itself contains softpipe/llvmpipe and
doesn't load any drivers either.

Marek