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SubjectRe: [PATCH v4 00/10] arm, arm64, cpufreq: frequency- and cpu-invariant accounting support for task scheduler
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On Friday, August 25, 2017 4:31:56 PM CEST Dietmar Eggemann wrote:
> For a more accurate (i.e. frequency- and cpu-invariant) accounting
> the task scheduler needs a frequency-scaling and on a heterogeneous
> system a cpu-scaling correction factor.
>
> This patch-set implements a Frequency Invariance Engine (FIE)
> based on the ratio of current frequency and maximum supported frequency
> (topology_get_freq_scale()) in the arch topology driver (arm, arm64) to
> provide such a frequency-scaling correction factor.
> This is a solution to get frequency-invariant accounting support for
> platforms without hardware-based performance tracking.
>
> The Cpu Invariance Engine (CIE) (topology_get_cpu_scale()) providing a
> cpu-scaling correction factor was already introduced by the "Fix issues
> and factorize arm/arm64 capacity information code" patch-set [1] and is
> currently part of v4.13-rc6.
>
> This patch-set also enables the frequency- and cpu-invariant accounting
> support. Enabling here means to associate (wire) the task scheduler
> function name arch_scale_freq_capacity and arch_scale_cpu_capacity with
> the FIE and CIE function names from drivers/base/arch_topology.c. This
> replaces the scheduler's default FIE and CIE in kernel/sched/sched.h.
>
> v3: review results:
>
> Viresh Kumar asked me during the v3 [2] review to move the definition
> of the default frequency-invariance setter arch_set_freq_scale() in
> front of cpufreq_generic_init() and to get rid of the fancy function
> header.
>
> v2: review results:
>
> During the v2 [3] review we agreed that cpufreq core is not the right
> place to drive this kind of FIE. In case of a future fast-switching
> arm/arm64 cpufreq driver, a return value other than
> CPUFREQ_ENTRY_INVALID of the '->fast_switch' driver callback does not
> indicate that the new frequency has been set. So calling the FIE's
> setter function (arch_set_freq_scale()) in cpufreq_driver_fast_switch()
> would not be correct.
>
> Instead this version of the patch-set assumes that the FIE setter
> function is provided by the cpufreq driver (slow- or fast-switching).
>
> Slow-switching driver:
>
> For a slow-switching driver the FIE setter function can be called in its
> '->target_index' driver callback, after a non-error return value from
> the (blocking) firmware call has been received.
> Two slow-switching cpufreq drivers (arm-big-little (exclusively used in
> arm/arm64) and cpufreq-dt) have been changed accordingly.
>
> Fast-switching driver:
>
> For a fast-switching driver the ARM System Control and Management
> Interface (SCMI) document [4] (4.5 Performance domain management
> protocol) provides an example for such a driver how to communicate with
> the firmware.
> It defines an optional performance domain related notification which
> indicates that the requested frequency has been changed. So the FIE
> setter function could be implemented here.
> In case the firmware does not implement this notification or the driver
> makes no use of it, the FIE setter would have to be placed in the
> '->fast_switch' driver callback assuming that the firmware has set the
> frequency.
>
> Weak arch_set_freq_scale() interface:
>
> Since a cpufreq driver (e.g. cpufreq-dt) can be build for different
> arch's a default (empty) implementation of the FIE setter function in
> cpufreq core is still needed for those arch's which do not implement it.
>
> FIE/CIE inlining:
>
> The FIE (topology_get_freq_scale()) and CIE (topology_get_cpu_scale())
> getter functions have been coded as static inline functions so they can
> be inlined into the scheduler fast path (e.g. __update_load_avg_se()).
>
> +------------------------------+ +------------------------------+
> | | | |
> | cpufreq: | | arch: |
> | | | |
> | weak arch_set_freq_scale() {}| | |
> | | | |
> +------------------------------+ | |
> | |
> +------------------------------+ | |
> | | | |
> | cpufreq driver: | | |
> | | | |
> | +-----------> arch_set_freq_scale() |
> | | | |
> +------------------------------+ | topology_set_cpu_scale() |
> | |
> +------------------------------+ | |
> | | | |
> | task scheduler: | | |
> | | | |
> | arch_scale_freq_capacity() +-----------> topology_get_freq_scale() |
> | | | |
> | arch_scale_cpu_capacity() +-----------> topology_get_cpu_scale() |
> | | | |
> +------------------------------+ +------------------------------+
>
> v1 review results:
>
> During the v1 [5] review Viresh Kumar pointed out that such a FIE based
> on cpufreq transition notifier will not work with future cpufreq
> policies supporting fast frequency switching.
> To include support for fast frequency switching policies the FIE
> implementation has been changed. Whenever there is a frequency change
> cpufreq now calls the arch specific function arch_set_freq_scale() which
> has to be implemented by the architecture. In case the arch does not
> specify this function FIE support is compiled out of cpufreq.
> The advantage is that this would support fast frequency switching since
> it does not rely on cpufreq transition (or policy) notifier anymore.
>
> Patch high level description:
>
> [ 01/10] Fix to free cpumask cpus_to_visit
> [ 02/10] Default (empty, weak) arch_set_freq_scale() implementation
> [03,04/10] Call arch_set_freq_scale() from two cpufreq drivers
> (arm_big_little and cpufreq-dt)
> [ 05/10] FIE
> [ 06/10] Allow CIE inlining
> [07,08/10] Enable frequency- and cpu-invariant accounting on arm
> [09,10/10] Enable frequency- and cpu-invariant accounting on arm64
>
> Changes v3->v4:
>
> - Rebase on top of v4.13-rc6
> - Move definition of arch_set_freq_scale() in cpufreq.c [02/10]
> - Add Acked-by for [01/10, 03-08/10]
>
> Changes v2->v3:
>
> - Rebase on top of v4.13-rc2
> - Fix 'notifier unregister'-'free cpumask' order in
> parsing_done_workfn() in [01/10]
> - Call arch_set_freq_scale() from cpufreq drivers (arm-big-little
> and cpufreq-dt) [02-04/10]
> - Allow inlining of topology_get_freq_scale() and
> topology_get_cpu_scale() into task scheduler fastpath [05,06/10]
>
> Changes v1->v2:
> - Rebase on top of next-20170630
> - Add fixup patch to free cpumask cpus_to_visit [01/10]
> - Propose solution to support fast frequency switching [02-04,07/10]
> - Add patch to allow CIE and FIE inlining [10/10]
>
> The patch-set is based on top of v4.13-rc6 and is also available from:
>
> git://linux-arm.org/linux-de.git upstream/freq_and_cpu_inv_v4
>
> Testing:
>
> The patch-set has been tested on TC2 (arm, arm-big-little driver), JUNO
> (arm64, arm-big-little driver) and Hikey620 (arm64, cpufreq-dt driver)
> by running a ramp-up rt-app task pinned to a cpu with the ondemand
> cpufreq governor and checking the load-tracking signals of this task.
>
> Driver module loading has been tested on TC2, JUNO and Hikey620 as well.
>
> [1] https://marc.info/?l=linux-kernel&m=149625018223002&w=2
> [2] https://marc.info/?l=linux-kernel&m=150118402232039&w=2
> [3] https://marc.info/?l=linux-pm&m=149933474313566&w=2
> [4] http://arminfo.emea.arm.com/help/topic/com.arm.doc.den0056a/DEN0056A_System_Control_and_Management_Interface.pdf
> [5] https://marc.info/?l=linux-kernel&m=149690865010019&w=2
>
> Dietmar Eggemann (10):
> drivers base/arch_topology: free cpumask cpus_to_visit
> cpufreq: provide default frequency-invariance setter function
> cpufreq: arm_big_little: invoke frequency-invariance setter function
> cpufreq: dt: invoke frequency-invariance setter function
> drivers base/arch_topology: provide frequency-invariant accounting
> support
> drivers base/arch_topology: allow inlining cpu-invariant accounting
> support
> arm: wire frequency-invariant accounting support up to the task
> scheduler
> arm: wire cpu-invariant accounting support up to the task scheduler
> arm64: wire frequency-invariant accounting support up to the task
> scheduler
> arm64: wire cpu-invariant accounting support up to the task scheduler
>
> arch/arm/include/asm/topology.h | 8 ++++++++
> arch/arm64/include/asm/topology.h | 8 ++++++++
> drivers/base/arch_topology.c | 29 +++++++++++++++++++++++------
> drivers/cpufreq/arm_big_little.c | 10 +++++++++-
> drivers/cpufreq/cpufreq-dt.c | 12 ++++++++++--
> drivers/cpufreq/cpufreq.c | 6 ++++++
> include/linux/arch_topology.h | 18 +++++++++++++++++-
> include/linux/cpufreq.h | 3 +++
> 8 files changed, 84 insertions(+), 10 deletions(-)
>
>

FWIW, patches [2-4/10] in this series are fine by me, but I guess you
need to talk to Viresh about the [3-4/10] anyway.

Thanks,
Rafael


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