On 24.11.2015 15:02, Moritz Barsnick wrote:
Hi D,
On Tue, Nov 24, 2015 at 14:31:58 +0100, D wrote:
I played setting the values higher but it was neither faster nor slower.
Average 4 cores utilization is still ~80%.
BTW, how do you define "utilization"? I believe in "top", 100% equals
one core's usage, so you should be able to achieve 400%. Below, you use
the term "100% on all 4 cores".
The 80% figure was a bit too high BTW, it's rather between 60 and 75%.
In top it jumps between ~230 and ~270%.
That said: I don't know much about libvpx, but this page:
http://wiki.webmproject.org/ffmpeg/vp9-encoding-guide
and more explicitly this one:
https://github.com/Kagami/webm.py/wiki/Notes-on-encoding-settings
says to use "-tile-columns" along with "-threads".
-tile-columns slightly affects output quality but it's the only
mechanism in VP9 to provide multithread encoding and decoding.
According to that, "-tile-columns" apparently defaults to 6. OTOH
"ffmpeg -h" says "-1", which corresponds to not explicitly setting it
to the encoder. And according to the encoder's sources:
By default, the value is 0, i.e. one single column tile for entire
image.
So 6 (correspnding to 2^6 columns) is likely not the default, but 0
(corresponding to 1 column), which is not beneficial to threading.
Disclaimer, again: I know nothing much about libvpx or VP9. ;-)
Changing "-tile-columns" to 0 does indeed use only on core (100%).
Setting it to 6 (maximal value), does not change anything (maybe because
6 is already the default value if it is correct). Other values do not
improve the 60-75% figure (that's all 4 cores or ~250% in top) too.
Moritz
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