Vishwa, Have you had a chance to do some usetime tests with these changes? It would be interesting to measure the power consumption with and without these changes. /Amit On Tue, Nov 23, 2010 at 5:59 PM, Vishwanath Sripathy <vishwanath.sripathy@xxxxxxxxxx> wrote: > Thanks David for the inputs. > I tried your patch. In addition to that I reduced transition_latency. > With these 2 changes, I do see much better results (worst case > performance of ondemand is 88%). > > Vishwa > > > On Mon, Nov 22, 2010 at 9:39 PM, David C Niemi <dniemi@xxxxxxxxxxxx> wrote: >> The general problem here is that the ondemand governor is aimed more at >> power savings than performance. In cases where the ondemand governor >> performs worse than the performance governor, the "sampling_down_factor" >> tunable is often useful. I submitted the patch to add this tunable a >> few weeks ago and it was acked by Venki, but I don't know what happened >> to it after that. It helps in two ways: >> >> 1) the governor does not spend as much overhead on the governor when the >> CPU is truly busy >> >> 2) the governor is a lot less eager to downshift when the CPU is busy -- >> without this patch, even on a busy system ondemand will blip down in >> clock speed surprisingly often, hurting performance. >> >> This patch is all about improving peak load performance. On quite a few >> loads I've tried this patch with a sampling_down_factor of 100 matches >> the performance governor quite well while the original ondemand >> performance was poor. On the other hand, it is not much help if you are >> trying to minimize power consumption on light to medium loads. If you >> set sampling_down_factor to "1" it preserves default behavior. >> >> David C Niemi >> >> Vishwanath Sripathy wrote: >>> Hi, >>> >>> I was trying to investigate performance issues that we were seeing >>> with some usecases like Video playback on OMAP Platforms with ondemand >>> governor. >>> As part of this, I found a tool called cpufreq-bench >>> (http://lwn.net/Articles/339862) which can be used determine the >>> performance impact of ondemand governor compared to performacne >>> governor. >>> When I ran this tool on OMAP3 (ZOOM3) platform using 2.6.36 kernel >>> with below command, the worstcase ondemand performance is 35% compared >>> to performance governor. >>> cpufreq-bench -l 50000 -s 100000 -x 50000 -y 100000 -g ondemand -r 5 -n 5 -v >>> >>> I tried the same on x86 platforms and there the worstcase performance >>> is around 88%. >>> Attached are the cpufreq-bench logs for x86 and omap3. >>> >>> Questions: >>> 1. Is this is known limitaiton of ondemand governor? >>> 2. How do we support system usecases (like video playback etc) with >>> ondemand governor if governor is not able to scale the frequencies in >>> realtime? Are applications expected to play with scaling_min_freq to >>> increase mpu frequency? >>> >>> Regards >>> Vishwa >> >> > > _______________________________________________ > linaro-dev mailing list > linaro-dev@xxxxxxxxxxxxxxxx > http://lists.linaro.org/mailman/listinfo/linaro-dev > -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
