benchmark encoding time with alignment

[bmegli]

From #12 on SBC (LattePanda Alpha) we were quite close to using whole time between frames for encoding

By forcing highest quality for depth and using default for IR:

• GPU usage reaches 50%
• CPU no changes (<35% of 400%)
• encode/send takes 20-23 ms

This left around 10 ms window at 30 FPS.

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If alignment takes considerable time there are several options:

• perform alignment during encoding
  • depending on alignment direction we may align during encoding target
  • but this will not work well along MLSP#12
  • unless order of frames (depth/color) will be made flexible
• perform alignment on receiving side (not sending)
  • decoding is much faster, so we have more free time
  • decoding side is usually more powerful
• do not force highest quality encoding on depth (e.g. return to default)

[bmegli]

Scenario:

• testing 307d8a9 RNHVE bench-align-time branch
• with LattePanda Alpha (KabyLake m3-7y30) as sender
• with i7-7820HK laptop as sender
• both on Ubuntu 18.04

848x480@30 fps, 8Mb + 1 Mb bitrate, alignment to color

./realsense-nhve-depth-color 192.168.0.100 9768 color 848 480 848 480 30 500 /dev/dri/renderD128 8000000 1000000 0.0000125

• CPU usage measured with htop

[bmegli]

Results

Laptop (KabyLake i7-7820HK)

Alignment enabled:

• 45-50% CPU
• align 3-11 ms
• align + encode + send 21-31 ms

Alignment commented out:

• 27-30% CPU
• encode + send time 17-19 ms

LattePanda Alpha (KabyLake m3-7y30)

Alignment enabled

• 46-56 % CPU
• align 5-16 ms (typically 5-8 ms)
• align + encode + send 24-36 ms (typically < 30 ms)

Alignment commented out:

• 39-43% CPU
• encode + send time 21-25 ms

[bmegli]

Discussion

• alignment time order of 5-10 ms
• has effect on latency
• on SBC we barely keep up with the data at 30 FPS (33 ms)

At this point, adding anything to the pipeline on SBC (e.g. post-processing) will require changes (already discussed in the first post).

Alignment time is quite inconsistent, should not be (e.g. 5-16 ms?). This probably means that the process is sometimes preempted during alignment.

For now it may stay as is but has to be kept in mind.