P4man had the right idea: as long as CPU frequency management is enabled, stressing the CPU will force it to run at max speed that is also beneficial to miner SW. Additionally, DeathAndTaxes clarified the reliability of mid-term hash-rate measures that need to be considered to estimate the potential improvement.
I observed something I fail to fully understand and post here for you to confirm and maybe take advantage of.
Recently I had to generate some personalized addresses with vanitygen. I first ran it on my laptop but soon found it not acceptable, since it will take days and generate heat and noise in my office. The only thing keeping me back to offload that task to the miner in my basement were doubts that it might negatively influence the mining performance.Tl;dr:
it did not, stressing the CPU increased my GPU hashing power by ~1%
Mining with Ubuntu and latest cgminer, my long term average hash-rate is about 1732MH/s (2*7970+1*6950). The CPU (Sempron 145) is mostly idling, system draws 750W at wall (not optimized: uses HD for cgminer development, not down-clocked CPU and GPU-mem, etc.).
After about an hour running vanitigen (100% CPU load: 97 for vanitigen, 2 for cgminer), the short term average increases by 1% to 1750MH/s. The power draw is then at 760W.
To eliminate some mid-term fluctuations caused by pool issues or local temperature extremes, I repeated the tests several times, either
- start and run it without vanitygen for ~2h, start vanitygen and see the average GH/s settling to a +1% average
- start and run with vanitygen runnng for ~2h, stop vanitygen and see the hashing power decreasing by 1%
I suspect this could be an effect of the CPU power saving features effective when CPU is idling and being disabled when CPU is fully loaded. Also, it might be that the Linux scheduler is more reactive when not entering the idle-task. Or some cgminer related thing that is specific to my setup.
Whatever, YMMV, but if you can reproduce, please share your results. With my low-scale setup the increased power cost roughly matches the performance gain, in higher scaled setups (e.g. 3*5970/6990) the gain might outperform the cost. Plus you can stress the CPU with mining instead of running vanitygen for some extra coins