Messages in this thread | | | Subject | Re: [PATCH v6 0/3] cpufreq: Replace timers with utilization update callbacks | From | Srinivas Pandruvada <> | Date | Wed, 10 Feb 2016 22:02:49 -0800 |
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On 02/10/2016 03:11 PM, Doug Smythies wrote: > On 2016.02.10 07:17 Rafael J. Wysocki wrote: >> On Friday, January 29, 2016 11:52:15 PM Rafael J. Wysocki wrote: >>> The following patch series introduces a mechanism allowing the cpufreq core >>> and "setpolicy" drivers to provide utilization update callbacks to be invoked >>> by the scheduler on utilization changes. Those callbacks can be used to run >>> the sampling and frequency adjustments code (intel_pstate) or to schedule the >>> execution of that code in process context (cpufreq core) instead of per-CPU >>> deferrable timers used in cpufreq today (which Thomas complained about during >>> the last Kernel Summit). > This patch set solves a long standing issue with the intel_pstate driver. > The issue began with the introduction of the "duration" method for deciding > if the CPU had been idle for a long time resulting in forcing the > target pstate downwards. Often this was the correct action, but sometimes this > was the wrong thing to do, because the cpu was actually very busy, but just so > happened to be idle on jiffy boundaries (perhaps similar to what Steve Muckle > was referring to on another branch of this thread). > > For an idle system, this patch set seems to change the maximum duration from > 4 seconds to 0.5 seconds for most CPUs. However, when using v1 of patches 1 > and 2 of 3 and v5 of 3 of 3, sometimes the durations (time between passes of > the intel-pstate driver for a given CPU) of upwards of 120 seconds were observed. > When patches 1, 2, and 3 of 3 v6 were used, the maximum observed durations of an > idle system were on the order of 500 milliseconds for most CPUs, but CPU 6 > sometimes went to 3.5 seconds and CPU 7 sometimes went to 4 seconds (small > sample space, I'll consider to run an overnight test for a much much larger > sample space). Note 4 seconds, is O.K., and what it was before, I'm just noting > it is all. > > I have a bunch of graphs, if anyone wants to see the supporting data. > > My test computer has an older model i7 (Intel(R) Core(TM) i7-2600K CPU @ 3.40GHz) Thanks Doug. If you have specific workloads, please compare performance.
- Srinivas > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-pm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >
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