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 > > -- 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
