linux-kernel - Re: [PATCH v6 0/6] V4L2 Explicit Synchronization

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Date:   Thu, 21 Dec 2017 16:49:31 -0200
From:   Mauro Carvalho Chehab <mchehab@....samsung.com>
To:     Gustavo Padovan <gustavo@...ovan.org>
Cc:     linux-media@...r.kernel.org, Hans Verkuil <hverkuil@...all.nl>,
        Shuah Khan <shuahkh@....samsung.com>,
        Pawel Osciak <pawel@...iak.com>,
        Alexandre Courbot <acourbot@...omium.org>,
        Sakari Ailus <sakari.ailus@....fi>,
        Brian Starkey <brian.starkey@....com>,
        Thierry Escande <thierry.escande@...labora.com>,
        linux-kernel@...r.kernel.org,
        Gustavo Padovan <gustavo.padovan@...labora.com>
Subject: Re: [PATCH v6 0/6] V4L2 Explicit Synchronization

Em Mon, 11 Dec 2017 16:27:35 -0200
Gustavo Padovan <gustavo@...ovan.org> escreveu:

> From: Gustavo Padovan <gustavo.padovan@...labora.com>
> 
> Hi,
> 
> One more iteration of the explicit fences patches, please refer
> to the previous version[1] for more details about the general
> mechanism
> 
> This version makes the patchset and the implementation much more
> simple, to start we are not using a ordered capability anymore,
> but instead we have a VIDIOC_ENUM_FMT flag to tell when the
> queue in not ordered. Drivers with ordered queues/formats don't
> need implement anything. See patches 1 and 2 for more details.
> 
> The implementation of in-fences and out-fences were condensed in
> just patches 4 and 5, making it more self-contained and easy to
> understand. See the patches for detailed changelog.
> 
> Please review! Thanks.

Hi Gustavo,

As I was afraid, the changes at the VB2 core makes it non-generic,
breaking support for the DVB VB2 patchset. That's a branch with
both patchsets applied:

	https://git.linuxtv.org/mchehab/experimental.git/log/?h=dvb_mmap%2bexplicit_fences


With the explicit fences patchset, the DVB streaming breaks:

	$ sudo perf stat dvbv5-zap -c ~/dvb_channel.conf "TV Brasilia RedeTV!"  -o /dev/null -t120 -R
	Usando demux 'dvb0.demux0'
	lendo canais do arquivo  '/home/mchehab/dvb_channel.conf'
	sintonizando em 557142857 Hz
	PID de vídeo 273
	  dvb_set_pesfilter 273
	PID de áudio 274
	  dvb_set_pesfilter 274
	Travado  (0x1f) Sinal= -85,22dBm C/N= 18,57dB UCB= 8589933955 pós-BER= 0
	Travado  (0x1f) Sinal= -85,24dBm C/N= 18,57dB UCB= 8589933955 pós-BER= 0
	Gravação iniciada para o arquivo '/dev/null'
	ERRO:DMX_REQBUFS failed: error=-1 (Invalid argument)
	ERRO:[stream_to_file] Failed to setup buffers!!! (Invalid argument)
	start streaming!!!
	copied 0 bytes (0 Kbytes/sec)
	Travado  (0x1f) Sinal= -85,25dBm C/N= 18,57dB UCB= 8589933955 pós-BER= 0

 Performance counter stats for 'dvbv5-zap -c /home/mchehab/dvb_channel.conf TV Brasilia RedeTV! -o /dev/null -t120 -R':

       7.001647  task-clock-msecs         #      0.003 CPUs 
            251  context-switches         #      0.036 M/sec
             18  CPU-migrations           #      0.003 M/sec
            181  page-faults              #      0.026 M/sec
       17001058  cycles                   #   2428.151 M/sec
       11342660  instructions             #      0.667 IPC  
         349075  cache-references         #     49.856 M/sec
          70802  cache-misses             #     10.112 M/sec

    2.133343557  seconds time elapsed

It also breaks support on V4L2, when fences is not used:

$ ./contrib/test/v4l2grab 
(kernel crashes)

I don't have a serial console on this machine to print what's
wrong, but clearly there's something not right there :-)

-- 
Thanks,
Mauro