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

Fri Apr 21 02:22:50 UTC 2017

On 21/04/17 09:01 AM, Marek Olšák wrote:
> On Thu, Apr 20, 2017 at 9:44 PM, gregory hainaut
> <gregory.hainaut at gmail.com> wrote:
>> On Thu, 20 Apr 2017 20:01:00 +0200
>> Marek Olšák <maraeo at gmail.com> wrote:
>>
>>> 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)?
>>
>> Hello Marek,
>>
>> No, I don't use the front buffer. I don't call glDrawBuffer for the FB 0. So I think,
>> it should use GL_BACK.
>> Hum except if some 3rparty libs do something in my back.
>>
>> In case it have any impact, I'm using either glXSwapIntervalEXT or glXSwapIntervalMESA (if the former wasn't found)
>> to control Vsync.
>>
>> If I understand you, you expect that DRI2GetBuffersWithFormat should haven't be called in the first place ?
> 
> It's OK for it to get called. We just have to find a way how to deal
> with it. If that means we have to disable old & slow DRI2 for
> glthread, that's fine. The other option is to sync the first draw call
> rendering to the default framebuffer.

FWIW, I think it should be possible to make DRI2GetBuffersWithFormat use
XCB directly.

There is other functionality related to events (window geometry changes,
GLX_INTEL_swap_event, maybe more?) for which DRI2 relies on libX11
specifics and can't use XCB directly. But hopefully that code can
already only run on the main thread.

-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer