On Wed, Mar 07, 2018 at 07:57:17PM +0100, Daniel Lezcano wrote: > >> The preliminary benchmarks show the following changes: > >> > >> On the hikey6220, dhrystone shows a throughtput increase of 40% for an > >> increase of the latency of 16% while sysbench shows a latency increase > >> of 5%. > > > > I don't follow these numbers. Throughput increase while injecting idle? > > compared to what? percentages of what? Please be more specific to better > > describer your work.. > > The dhrystone throughput is based on the virtual timer, when we are > running, it is at max opp, so the throughput increases. But regarding > the real time, it takes obviously more time to achieve as we are > artificially inserting idle cycles. With the cpufreq governor, we run at > a lower opp, so the throughput is less for dhrystone but it takes less > time to achieve. > > Percentages are comparing cpufreq vs cpuidle cooling devices. I will > take care of presenting the results in a more clear way in the next version.
I think we should also note that the current hikey settings for cpufreq are very badly tuned for this platform. It has a single temp threshold and it jumps from max freq to min freq. IIRC Leo's work on Hikey thermals correctly it would be much better if it used the power-allocator thermal governor or if if copied some of the Samsung 32-bit platform by configuring the step governor with a graduated with a slightly lower threshold that moves two stops back in the OPP table (which is still fairly high clock speed... but it thermally sustainable). Daniel. > >> Initially, the first version provided also the cpuidle + cpufreq combo > >> cooling device but regarding the latest comments, there is a misfit with > >> how the cpufreq cooling device and suspend/resume/cpu hotplug/module > >> loading|unloading behave together while the combo cooling device was > >> designed assuming the cpufreq cooling device was always there. This > >> dynamic is investigated and the combo cooling device will be posted > >> separetely after this series gets merged. > > > > Yeah, this is one of the confusing parts. Could you please > > remind us of the limitations here? Why can't we enable CPUfreq > > on higher trip points and CPUidle on lower trip points, for example? > > Sorry, I'm not getting the question. We don't want to enable cpuidle or > cpufreq at certain point but combine the cooling effect of both in order > to get the best tradeoff power / performance. > > Let me give an example with a simple SoC - one core. > > Let's say we have 4 OPPs and a core-sleep idle state. Respectively, the > OPPs consume 100mW, 500mW, 2W, 4W. Now the CPU is in an intensive work > running at the highest OPP, thus consuming 4W. The temperature increases > and reaches 75°C which is the mitigation point and where the sustainable > power is 1.7W. > > - With the cpufreq cooling device, we can't have 4W, so we go back and > forth between 2W and 500mW. > > - With the cpuidle cooling device, we are at the highest OPP (there is > no cpufreq driver) and we insert 47.5% of idle duration > > - With the combo cooling device, we compute the round-up OPP (here 2W) > and we insert idle cycles for the remaining power to reach the > sustainable power, so 15%. > > With the combo, we increase the performances for the same requested > power. There is no yet the state2power callbacks but we expect the > combination of dropping the static leakage and the higher OPP to give > better results in terms of performance and mitigation on energy eager > CPUs like the recent big ARM cpus with the IPA governor. > > Going straight to the point of your question above, we can see the > cpufreq cooling device and the cpuidle cooling device have to > collaborate. If we unregister the cpufreq device, we have to do the math > for the power again in the combo cooling device. It is not a problem by > itself but needs an extra reflexion in the current code. > > > Specially from a system design point of view, the system engineer > > typically would benefit of idle injections to achieve overall > > average CPU frequencies in a more granular fashion, for example, > > achieving performance vs. cooling between available real > > frequencies, avoiding real switches. > > > > Also, there is a major design question here. After Linaro's attempt > > to send a cpufreq+cpuidle cooling device(s), there was an attempt > > to generalize and extend intel powerclamp driver. > > I'm not aware of such attempt. > > > Do you mind > > explaining why refactoring intel powerclamp is not possible? Basic > > idea is the same, no? > > Basically the idea is the same: run synchronized idle thread and call > play_idle(). That is all. Putting apart the intel_powerclamp is very x86 > centric and contains a plethora of code not fitting our purpose, it > increases the idle duration while we are increasing the number of idle > cycles but keep the idle duration constant in order to have a control on > the latency for the user interactivity. If you compare the idle > injection threads codes (powerclamp and cpuidle cooling device), you > will also notice they are very different in terms of implementation. > > The combo cooling device collaborates with the cpufreq cooling device > and reuses the DT binding, and finally it uses the power information > provided in the DT. The idle injection is a brick to the combo cooling > device. > > Initially I thought we should refactor the intel_powerclamp but it > appears the combo cooling device reuses the cpufreq and cpuidle cooling > device, making sense to have them all in a single file and evolving to a > single cooling device with different strategies. > > > > >> Daniel Lezcano (7): > >> thermal/drivers/cpu_cooling: Fixup the header and copyright > >> thermal/drivers/cpu_cooling: Add Software Package Data Exchange (SPDX) > >> thermal/drivers/cpu_cooling: Remove pointless field > >> thermal/drivers/Kconfig: Convert the CPU cooling device to a choice > >> thermal/drivers/cpu_cooling: Add idle cooling device documentation > >> thermal/drivers/cpu_cooling: Introduce the cpu idle cooling driver > >> cpuidle/drivers/cpuidle-arm: Register the cooling device > >> > >> Documentation/thermal/cpu-idle-cooling.txt | 165 ++++++++++ > >> drivers/cpuidle/cpuidle-arm.c | 5 + > >> drivers/thermal/Kconfig | 30 +- > >> drivers/thermal/cpu_cooling.c | 480 > >> +++++++++++++++++++++++++++-- > >> include/linux/cpu_cooling.h | 15 +- > >> 5 files changed, 668 insertions(+), 27 deletions(-) > >> create mode 100644 Documentation/thermal/cpu-idle-cooling.txt > >> > >> -- > >> 2.7.4 > >> > > > -- > <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs > > Follow Linaro: <http://www.facebook.com/pages/Linaro> Facebook | > <http://twitter.com/#!/linaroorg> Twitter | > <http://www.linaro.org/linaro-blog/> Blog >
