Bad precision and warnings when running under Raspberry PI 3

This project is really promising. Too bad there is no documentation and very few examples 😃.

I was trying some examples and I see this:

root@osmcpi:/home/jcea/virtualenv/py-videocore/examples# ../../bin/python sgemm.py 
sgemm.py:655: VisibleDeprecationWarning: using a non-integer number instead of an integer will result in an error in the future
  uniforms[th, 4] = A.addresses()[i*16*h, 0]
sgemm.py:656: VisibleDeprecationWarning: using a non-integer number instead of an integer will result in an error in the future
  uniforms[th, 5] = B.addresses()[0, j*64*w]
sgemm.py:657: VisibleDeprecationWarning: using a non-integer number instead of an integer will result in an error in the future
  uniforms[th, 6] = C.addresses()[i*16*h, j*64*w]
==== sgemm example (96x363 times 363x3072) ====
threads: 12
numpy: 31.9355 sec, 0.0067 Gflops
GPU: 0.0321 sec, 6.7054 Gflops
maximum absolute error: 7.3559e+01

root@osmcpi:/home/jcea/virtualenv/py-videocore/examples# ../../bin/python sgemm_1thread.py 
==== sgemm example (96x363 times 363x3072) ====
threads: 1
numpy: 31.5038 sec, 0.0068 Gflops
GPU: 0.2676 sec, 0.8034 Gflops
maximum absolute error: 7.8866e+01

The virtualenv I am using runs Python 3.4.

The Raspberry PI 3 is running KODI at the same time, but not reproducing a video, just in the main menu.

“Hello world” example works fine, with maximum error ~1e-7.

Maybe this is useful:

root@osmcpi:/home/jcea/virtualenv/py-videocore/examples# ../../bin/python mailbox.py 
firmware revision: 57bc72be
board model: 0
board revision: a02082
board serial: 000000008a498dfc

[jcea]

Yes, I now get this:

==== sgemm example (96x363 times 363x3072) ====
threads: 12
numpy: 38.8727 sec, 0.0055 Gflops
GPU: 0.0282 sec, 7.6141 Gflops
minimum absolute error: 0.0000e+00
maximum absolute error: 9.1553e-04
minimum relative error: 0.0000e+00
maximum relative error: 1.0522e+01

I close the issue. Thanks.

PS: The NUMPY speed is a bit crappy because I have KODI running at the same time! 😃.

[patrickms]

On a Raspberry Pi 2 at least, the issue seems to be caused by the (default) disabling of the L2 cache.

Adding disable_l2cache=0 to /boot/config.txt (as well as commenting out dtoverlay=vc4-kms-v3d) and rebooting the Pi solved the problem for me.

See also https://raspberrypi.stackexchange.com/questions/36960/why-is-the-l2-cache-disabled-by-default-on-raspbian-jessie#36967