Re: [PATCH v1] media: videobuf2: Add new uAPI for DVB streaming I/O
From: Mauro Carvalho Chehab
Date: Thu Dec 21 2017 - 07:48:15 EST
Em Tue, 19 Dec 2017 09:05:53 +0530
Satendra Singh Thakur <satendra.t@xxxxxxxxxxx> escreveu:
> -Ported below mentioned patch to latest kernel:
> commit ace52288edf0 ("Merge tag 'for-linus-20171218' of
> git://git.infradead.org/linux-mtd")
>
> -Fixed few bugs in the patch, enhanced it and added polling
> --dvb_vb2.c:dvb_vb2_fill_buffer=>
> ----Set the size of the outgoing buffer after while loop using
> vb2_set_plane_payload
> ----Added NULL check for source buffer as per normal convention of
> demux driver, this is called twice, first time with valid buffer
> second time with NULL pointer, if its not handled, it will result in
> crash
> ---Restricted spinlock for only list_* operations
>
> --dvb_vb2.c:dvb_vb2_init=>
> ----Restricted q->io_modes to only VB2_MMAP as its the only
> supported mode
>
> --dvb_vb2.c:dvb_vb2_release=>Replaced the && in if condiion with &,
> because it was always getting satisfied.
>
> --dvb_vb2.c:dvb_vb2_stream_off=>Added list_del code for enqueud buffers
> upon stream off
>
> -Added polling functionality
> --dvb_vb2.c:dvb_vb2_poll=>added this function
> --dmxdev.c:dvb_demux_poll, dvb_dvr_poll=>Called dvb_vb2_poll from
> these functions
>
> -Ported this patch and latest videobuf2 to lower kernel versions and
> tested auto scan
>
> -Original patch=>
> --https://patchwork.linuxtv.org/patch/31613/
>
> Signed-off-by: Junghak Sung <jh1009.sung@xxxxxxxxxxx>
> Signed-off-by: Geunyoung Kim <nenggun.kim@xxxxxxxxxxx>
> Acked-by: Seung-Woo Kim <sw0312.kim@xxxxxxxxxxx>
> Acked-by: Inki Dae <inki.dae@xxxxxxxxxxx>
> Signed-off-by: Satendra Singh Thakur <satendra.t@xxxxxxxxxxx>
Thanks for the patch!
I applied it on the top of Kernel 4.14 and fixed one bug that were causing
an annoying WARN_ON() print.
Btw, as you wrote a poll() function, I suspect that you used some app to
test it. Care to ship the patches for your test application?
-
For now, I added on my experimental repository:
https://git.linuxtv.org/mchehab/experimental.git/log/?h=dvb_mmap
I also applied the testing patch from 2015 on this tree:
https://git.linuxtv.org/mchehab/experimental-v4l-utils.git/log/?h=dvb_mmap
I ended by rewriting the patch description to make it clearer/more
complete.
And I took some statistics using "perf stats" command, using a DiBcom 8000
ISDB-T device (Prolink Microsystems Corp. PV-D231U(RN)-F), running on an
Intel NUC D53427RKE with an i5-3427U CPU @ 1.80GHz (2 cores, 2 threads/core),
equipped with SSD disks.
Those are the results:
1) Writing to a file, using read() syscalls
Performance counter stats for 'dvbv5-zap -c /home/mchehab/dvb_channel.conf TV Brasilia RedeTV! -o /tmp/out -t120':
117.253780 task-clock-msecs # 0.001 CPUs
4593 context-switches # 0.039 M/sec
425 CPU-migrations # 0.004 M/sec
194 page-faults # 0.002 M/sec
284427111 cycles # 2425.739 M/sec
143947266 instructions # 0.506 IPC
11975002 cache-references # 102.129 M/sec
3571404 cache-misses # 30.459 M/sec
120.114989264 seconds time elapsed
2) Writing to a file, using mmap() syscalls
Performance counter stats for 'dvbv5-zap -c /home/mchehab/dvb_channel.conf TV Brasilia RedeTV! -o /tmp/out -t120 -R':
69.258796 task-clock-msecs # 0.001 CPUs
999 context-switches # 0.014 M/sec
190 CPU-migrations # 0.003 M/sec
182 page-faults # 0.003 M/sec
176921677 cycles # 2554.501 M/sec
125926300 instructions # 0.712 IPC
5053616 cache-references # 72.967 M/sec
3123259 cache-misses # 45.095 M/sec
120.235712497 seconds time elapsed
All performance indicators reduced. The most impressive ones are
the number of context switches, that reduced by about 4.5x, and the
number of cache references by about 2,5x!
3) Writing to /dev/null, using read() syscalls
Performance counter stats for 'dvbv5-zap -c /home/mchehab/dvb_channel.conf TV Brasilia RedeTV! -o /dev/null -t120':
67.633678 task-clock-msecs # 0.001 CPUs
4583 context-switches # 0.068 M/sec
113 CPU-migrations # 0.002 M/sec
199 page-faults # 0.003 M/sec
152635399 cycles # 2256.796 M/sec
30920291 instructions # 0.203 IPC
6273962 cache-references # 92.764 M/sec
1666393 cache-misses # 24.639 M/sec
4) writing to /dev/null, using mmap() syscalls
Performance counter stats for 'dvbv5-zap -c /home/mchehab/dvb_channel.conf TV Brasilia RedeTV! -o /dev/null -t120 -R':
19.198192 task-clock-msecs # 0.000 CPUs
991 context-switches # 0.052 M/sec
196 CPU-migrations # 0.010 M/sec
181 page-faults # 0.009 M/sec
44730100 cycles # 2329.912 M/sec
16348743 instructions # 0.365 IPC
794952 cache-references # 41.408 M/sec
348873 cache-misses # 18.172 M/sec
120.169979970 seconds time elapsed
Here, the gains are even more expressive:
- the number of task clocks reduced by 3,5 times;
- the number of context switches reduced by about 4,5 times;
- the number of CPU cycles reduced by almost 3,5 times;
- the number of executed instructions reduced almost 2 times;
- the number of cache references reduced by almost 8 times;
- the number of cache misses reduced more than 4,5 times.
There was a small penalty to pay: the number of CPU migrations
increased by about 3/4, but that's explainable by the fact that
now, the CPU usage is a lot less, and the scheduler optimized the
code to use more CPUs.
In summary, from what I tested so far, the results are impressive,
even considering that I tested with an USB device!
I'll keep running more tests here and preparing this patchset to be
merged upstream.
Thanks,
Mauro