| Message ID | 20200327095703.93178-1-linus.walleij@linaro.org (mailing list archive) |
|---|---|
| State | Changes Requested |
| Headers | show |
| Series | ARM: vexpress: Make schedutil governor available | expand |
On Fri, Mar 27, 2020 at 10:57 AM Linus Walleij <linus.walleij@linaro.org> wrote: > > When building the kernel for Versatile Express we need to > consider that some of these boards are big.LITTLE HMP > systems. > > As can be seen from kernel/sched/topology.c: > > "EAS can be used on a root domain if it meets all the following conditions: > 1. an Energy Model (EM) is available; > 2. the SD_ASYM_CPUCAPACITY flag is set in the sched_domain hierarchy. > 3. no SMT is detected. > 4. the EM complexity is low enough to keep scheduling overheads low; > 5. schedutil is driving the frequency of all CPUs of the rd;" > > This means that at the very least, schedutil needs to be > available as a scheduling policy for EAS to work on these > systems. Make this explicit by selecting CPU_FREQ and > CPU_FREQ_GOV_SCHEDUTIL from the Versatile Express > machine. > > Currently users of the TC2 board (like me) has to figure these > dependencies out themselves and it is not helpful. > > It is still necessary to configure in the schedutil as default > governor manually to actually get a working b.L system, so this > just makes the right governor available to b.L systems, it does > not turn it on by default. > > Cc: Vincent Guittot <vincent.guittot@linaro.org> > Cc: Viresh Kumar <viresh.kumar@linaro.org> > Cc: Sudeep Holla <sudeep.holla@arm.com> > Signed-off-by: Linus Walleij <linus.walleij@linaro.org> Hi Linus, I agree we should make it available by default on platforms that need it for big.LITTLE, but I don't like the idea of selecting the governor from a platform Kconfig file, as generally speaking it leads to more problems when user-visible options are selected like this. What I could imagine doing however would be to change the cpufreq selection to use schedutil by default if CONFIG_BIG_LITTLE is set, like: choice prompt "Default CPUFreq governor" default CPU_FREQ_DEFAULT_GOV_SCHEDUTIL if BIG_LITTLE default CPU_FREQ_DEFAULT_GOV_USERSPACE if ARM_SA1100_CPUFREQ || ARM_SA1110_CPUFREQ default CPU_FREQ_DEFAULT_GOV_PERFORMANCE help This option sets which CPUFreq governor shall be loaded at startup. If in doubt, select 'performance'. and then changing CONFIG_BIG_LITTLE to be enabled by default on any platform that uses that configuration. If CONFIG_BIG_LITTLE is too overloaded already (I can't tell exactly what this is used for), a new symbol could be added for what we want here. Arnd
On 27-03-20, 10:57, Linus Walleij wrote: > When building the kernel for Versatile Express we need to > consider that some of these boards are big.LITTLE HMP > systems. > > As can be seen from kernel/sched/topology.c: > > "EAS can be used on a root domain if it meets all the following conditions: > 1. an Energy Model (EM) is available; > 2. the SD_ASYM_CPUCAPACITY flag is set in the sched_domain hierarchy. > 3. no SMT is detected. > 4. the EM complexity is low enough to keep scheduling overheads low; > 5. schedutil is driving the frequency of all CPUs of the rd;" > > This means that at the very least, schedutil needs to be > available as a scheduling policy for EAS to work on these > systems. Make this explicit by selecting CPU_FREQ and > CPU_FREQ_GOV_SCHEDUTIL from the Versatile Express > machine. > > Currently users of the TC2 board (like me) has to figure these > dependencies out themselves and it is not helpful. > > It is still necessary to configure in the schedutil as default > governor manually to actually get a working b.L system, so this > just makes the right governor available to b.L systems, it does > not turn it on by default. > > Cc: Vincent Guittot <vincent.guittot@linaro.org> > Cc: Viresh Kumar <viresh.kumar@linaro.org> > Cc: Sudeep Holla <sudeep.holla@arm.com> > Signed-off-by: Linus Walleij <linus.walleij@linaro.org> > --- > arch/arm/mach-vexpress/Kconfig | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/arch/arm/mach-vexpress/Kconfig b/arch/arm/mach-vexpress/Kconfig > index 726a68085c3b..0a5a67448c94 100644 > --- a/arch/arm/mach-vexpress/Kconfig > +++ b/arch/arm/mach-vexpress/Kconfig > @@ -8,6 +8,8 @@ menuconfig ARCH_VEXPRESS > select ARM_GLOBAL_TIMER > select ARM_TIMER_SP804 > select COMMON_CLK_VERSATILE > + select CPU_FREQ > + select CPU_FREQ_GOV_SCHEDUTIL > select GPIOLIB > select HAVE_ARM_SCU if SMP > select HAVE_ARM_TWD if SMP Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
diff --git a/arch/arm/mach-vexpress/Kconfig b/arch/arm/mach-vexpress/Kconfig index 726a68085c3b..0a5a67448c94 100644 --- a/arch/arm/mach-vexpress/Kconfig +++ b/arch/arm/mach-vexpress/Kconfig @@ -8,6 +8,8 @@ menuconfig ARCH_VEXPRESS select ARM_GLOBAL_TIMER select ARM_TIMER_SP804 select COMMON_CLK_VERSATILE + select CPU_FREQ + select CPU_FREQ_GOV_SCHEDUTIL select GPIOLIB select HAVE_ARM_SCU if SMP select HAVE_ARM_TWD if SMP
When building the kernel for Versatile Express we need to consider that some of these boards are big.LITTLE HMP systems. As can be seen from kernel/sched/topology.c: "EAS can be used on a root domain if it meets all the following conditions: 1. an Energy Model (EM) is available; 2. the SD_ASYM_CPUCAPACITY flag is set in the sched_domain hierarchy. 3. no SMT is detected. 4. the EM complexity is low enough to keep scheduling overheads low; 5. schedutil is driving the frequency of all CPUs of the rd;" This means that at the very least, schedutil needs to be available as a scheduling policy for EAS to work on these systems. Make this explicit by selecting CPU_FREQ and CPU_FREQ_GOV_SCHEDUTIL from the Versatile Express machine. Currently users of the TC2 board (like me) has to figure these dependencies out themselves and it is not helpful. It is still necessary to configure in the schedutil as default governor manually to actually get a working b.L system, so this just makes the right governor available to b.L systems, it does not turn it on by default. Cc: Vincent Guittot <vincent.guittot@linaro.org> Cc: Viresh Kumar <viresh.kumar@linaro.org> Cc: Sudeep Holla <sudeep.holla@arm.com> Signed-off-by: Linus Walleij <linus.walleij@linaro.org> --- arch/arm/mach-vexpress/Kconfig | 2 ++ 1 file changed, 2 insertions(+)