Messages in this thread | | | Subject | Re: [PATCH 0/3] cpufreq: Replace timers with utilization update callbacks | From | Srinivas Pandruvada <> | Date | Wed, 3 Feb 2016 16:08:02 -0800 |
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On 02/03/2016 02:20 PM, Rafael J. Wysocki wrote: > On Friday, January 29, 2016 11:52:15 PM Rafael J. Wysocki wrote: >> Hi, >> >> 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). >> >> [1/3] Introduce a mechanism for calling into cpufreq from the scheduler and >> registering callbacks to be executed from there. >> >> [2/3] Modify intel_pstate to use the mechanism introduced by [1/3] instead >> of per-CPU deferrable timers to do its work. >> >> This isn't entirely straightforward as the scheduler context running those >> callbacks is really special. Among other things it can only use raw >> spinlocks and cannot invoke wake_up_process() directly. Also, calling >> ktime_get() from there may be too expensive on some systems. All that has to >> be taken into account, but even then the change allows some lines of code to be >> cut from the driver. >> >> Some performance and energy consumption measurements have been carried out with >> an earlier version of this patch and it looks like the changes lead to a >> slightly better performing system that consumes slightly less energy at the >> same time overall. >> >> [3/3] Modify the cpufreq core to use the mechanism introduced by [1/3] instead >> of per-CPU deferrable timers to queue up the execution of governor work. >> >> Again, this isn't really straightforward for the above reasons, but still the >> code size is reduced a bit by the changes. >> >> I'm still unsure about the energy consumption and performance impact of [3/3] >> as earlier versions of it led to inconsistent results (most likely due to bugs >> in them that hopefully have been fixed in this version). In particular, the >> additional irq_work may turn out to be problematic, but more optimizations are >> possible on top of this one even if it makes things worse by itself. >> >> For example, it should be possible to move the execution of state selection >> code into the utilization update callback itself, at least in principle, for >> all governors. The P-state/OPP adjustment may need to be run from process >> context still, but for the drivers that can do it without sleeping it should >> be possible to move that into the utilization update callback as well. >> >> The patches are on top of 4.5-rc1 and have been tested on a couple of x86 >> machines. > Well, no responses here, so I'm inclined to believe that this series is fine > by everybody (at least by everybody in the CC). > > I can wait for a few days more, but new material is starting to pile up on top > of these patches and I'll simply need to move forward at one point. Based on the test results for intel_pstate and acpi_cpufreq, I don't see any problem in applying these patches.
Thanks, Srinivas > Thanks, > Rafael > > -- > 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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