[Skiboot] [PATCH] SLW : Increase stop4-5 residency by 5x

[Klaus Heinrich Kiwi]

On 11/21/2019 9:10 AM, Abhishek Goel wrote:
> Using ppdcf2d run, we observed that there was a drop of about 50%
> throughput with stop4/5. In this benchmark the GPU waits on the cpu to
> wakeup and provide the subsequent data block to compute. CPUs serving
> GPUs workloads are idle enough for the current residency values for the
> governor to pick up stop4/5 states for those CPUs. The higher wakeup
> latency of these deep states accumulates over the run and shows up as a
> performance drop.
>
> We observe no perfromance drop with increased residency values.

Do we know or can we estimate what are the power-saving drawbacks from 
such a change? Why did we choose 10ms to begin with? If this is a corner 
case, wouldn't it be better if that was a runtime choice, or in the 
extreme case disable powersave altogether?

-Klaus

-- 
Klaus Heinrich Kiwi <klaus at linux.vnet.ibm.com>