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    Subject[PATCH v4 02/24] sched: Add interfaces for IPC classes
    Date
    Add the interfaces that architectures shall implement to convey the data
    to support IPC classes.

    arch_update_ipcc() updates the IPC classification of the current task as
    given by hardware.

    arch_get_ipcc_score() provides a performance score for a given IPC class
    when placed on a specific CPU. Higher scores indicate higher performance.

    When a driver or equivalent enablement code has configured the necessary
    hardware to support IPC classes, it should call sched_enable_ipc_classes()
    to notify the scheduler that it can start using IPC classes data.

    The number of classes and the score of each class of task are determined
    by hardware.

    Cc: Ben Segall <bsegall@google.com>
    Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
    Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
    Cc: Ionela Voinescu <ionela.voinescu@arm.com>
    Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
    Cc: Len Brown <len.brown@intel.com>
    Cc: Lukasz Luba <lukasz.luba@arm.com>
    Cc: Mel Gorman <mgorman@suse.de>
    Cc: Perry Yuan <Perry.Yuan@amd.com>
    Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
    Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Tim C. Chen <tim.c.chen@intel.com>
    Cc: Valentin Schneider <vschneid@redhat.com>
    Cc: Zhao Liu <zhao1.liu@linux.intel.com>
    Cc: x86@kernel.org
    Cc: linux-pm@vger.kernel.org
    Cc: linux-kernel@vger.kernel.org
    Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
    ---
    Changes since v3:
    * None

    Changes since v2:
    * Clarified the properties of the IPC score: abstract, and linear. It can
    normalized when needed. (Ionela)
    * Selected a better default IPC score. (Ionela)
    * Removed arch_has_ipc_classes(). It is not suitable for hardware that is
    not ready to support IPC classes after boot. (Lukasz)
    * Added a new sched_enable_ipc_classes() interface that drivers or
    enablement code can call when ready to support IPC classes. (Lukasz)

    Changes since v1:
    * Shortened the names of the IPCC interfaces (PeterZ):
    sched_task_classes_enabled >> sched_ipcc_enabled
    arch_has_task_classes >> arch_has_ipc_classes
    arch_update_task_class >> arch_update_ipcc
    arch_get_task_class_score >> arch_get_ipcc_score
    * Removed smt_siblings_idle argument from arch_update_ipcc(). (PeterZ)
    ---
    include/linux/sched/topology.h | 6 ++++
    kernel/sched/sched.h | 66 ++++++++++++++++++++++++++++++++++
    kernel/sched/topology.c | 9 +++++
    3 files changed, 81 insertions(+)

    diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h
    index 816df6cc444e..5b084d3c9ad1 100644
    --- a/include/linux/sched/topology.h
    +++ b/include/linux/sched/topology.h
    @@ -280,4 +280,10 @@ static inline int task_node(const struct task_struct *p)
    return cpu_to_node(task_cpu(p));
    }

    +#ifdef CONFIG_IPC_CLASSES
    +extern void sched_enable_ipc_classes(void);
    +#else
    +static inline void sched_enable_ipc_classes(void) { }
    +#endif
    +
    #endif /* _LINUX_SCHED_TOPOLOGY_H */
    diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
    index 556496c77dc2..03fb53e9f340 100644
    --- a/kernel/sched/sched.h
    +++ b/kernel/sched/sched.h
    @@ -2544,6 +2544,72 @@ void arch_scale_freq_tick(void)
    }
    #endif

    +#ifdef CONFIG_IPC_CLASSES
    +DECLARE_STATIC_KEY_FALSE(sched_ipcc);
    +
    +static inline bool sched_ipcc_enabled(void)
    +{
    + return static_branch_unlikely(&sched_ipcc);
    +}
    +
    +#ifndef arch_update_ipcc
    +/**
    + * arch_update_ipcc() - Update the IPC class of the current task
    + * @curr: The current task
    + *
    + * Request that the IPC classification of @curr is updated.
    + *
    + * Returns: none
    + */
    +static __always_inline
    +void arch_update_ipcc(struct task_struct *curr)
    +{
    +}
    +#endif
    +
    +#ifndef arch_get_ipcc_score
    +
    +#define SCHED_IPCC_SCORE_SCALE (1L << SCHED_FIXEDPOINT_SHIFT)
    +/**
    + * arch_get_ipcc_score() - Get the IPC score of a class of task
    + * @ipcc: The IPC class
    + * @cpu: A CPU number
    + *
    + * The IPC performance scores reflects (but it is not identical to) the number
    + * of instructions retired per cycle for a given IPC class. It is a linear and
    + * abstract metric. Higher scores reflect better performance.
    + *
    + * The IPC score can be normalized with respect to the class, i, with the
    + * highest IPC score on the CPU, c, with highest performance:
    + *
    + * IPC(i, c)
    + * ------------------------------------ * SCHED_IPCC_SCORE_SCALE
    + * max(IPC(i, c) : (i, c))
    + *
    + * Scheduling schemes that want to use the IPC score along with other
    + * normalized metrics for scheduling (e.g., CPU capacity) may need to normalize
    + * it.
    + *
    + * Other scheduling schemes (e.g., asym_packing) do not need normalization.
    + *
    + * Returns the performance score of an IPC class, @ipcc, when running on @cpu.
    + * Error when either @ipcc or @cpu are invalid.
    + */
    +static __always_inline
    +unsigned long arch_get_ipcc_score(unsigned short ipcc, int cpu)
    +{
    + return SCHED_IPCC_SCORE_SCALE;
    +}
    +#endif
    +#else /* CONFIG_IPC_CLASSES */
    +
    +#define arch_get_ipcc_score(ipcc, cpu) (-EINVAL)
    +#define arch_update_ipcc(curr)
    +
    +static inline bool sched_ipcc_enabled(void) { return false; }
    +
    +#endif /* CONFIG_IPC_CLASSES */
    +
    #ifndef arch_scale_freq_capacity
    /**
    * arch_scale_freq_capacity - get the frequency scale factor of a given CPU.
    diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
    index ca4472281c28..c3a633a4b474 100644
    --- a/kernel/sched/topology.c
    +++ b/kernel/sched/topology.c
    @@ -672,6 +672,15 @@ DEFINE_PER_CPU(struct sched_domain __rcu *, sd_asym_packing);
    DEFINE_PER_CPU(struct sched_domain __rcu *, sd_asym_cpucapacity);
    DEFINE_STATIC_KEY_FALSE(sched_asym_cpucapacity);

    +#ifdef CONFIG_IPC_CLASSES
    +DEFINE_STATIC_KEY_FALSE(sched_ipcc);
    +
    +void sched_enable_ipc_classes(void)
    +{
    + static_branch_enable_cpuslocked(&sched_ipcc);
    +}
    +#endif
    +
    static void update_top_cache_domain(int cpu)
    {
    struct sched_domain_shared *sds = NULL;
    --
    2.25.1
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