On Mon, Nov 29, 2010 at 6:36 PM, Amit Kucheria amit.kucheria@linaro.org wrote:
On Mon, Nov 29, 2010 at 3:58 AM, Michael Hope michael.hope@linaro.org wrote:
I sat down and measured the power consumption of the NEON unit on an OMAP3. Method and results are here: https://wiki.linaro.org/MichaelHope/Sandbox/NEONPower
The board takes 2.37 W and the NEON unit adds an extra 120 mW. Assuming the core takes 1 W, then the code needs to run 12 % faster with NEON on to be a net power win.
Note that the results are inaccurate but valid enough.
Thanks for doing this Michael. Very interesting numbers. Some questions/comments:
- What is the load on the system when running your loop?
It's the only process running, so the load average should be 1.
- 2.73W for the board certainly means no PM. So the actual cost of NEON
will be higher when you run a kernel with working PM.
Yip, but the absolute cost should be the same. The interesting question is: given a workload that takes, say X CPU seconds at full power, how much faster does the NEON version have to be to use less total energy?
- What percentage of the packages in the main repo of Ubuntu generate NEON?
Very few at the moment. Only the ones that have NEON specific backends really, but that includes X via pixman and any video or audio decoders.
-- Michael