详解 ARM PMU (Performance Monitoring Unit)

本文会详细讲解ARM PMU模块原理及代码流程

kernel version=4.14.90, arch=arm64

初始化流程：

arch/arm64/kernel/perf_event.cdevice_initcall(armv8_pmu_driver_init)

这里使用device_initcall调用进行函数的初始化流程，关于device_initcall的定义及实现流程再额外研究，这里简单列一下initcall系列函数的调用顺序

include/linux/init.h#define pure_initcall(fn)        __define_initcall(fn, 0)#define core_initcall(fn)        __define_initcall(fn, 1)
#define core_initcall_sync(fn)        __define_initcall(fn, 1s)
#define postcore_initcall(fn)        __define_initcall(fn, 2)
#define postcore_initcall_sync(fn)    __define_initcall(fn, 2s)
#define arch_initcall(fn)        __define_initcall(fn, 3)
#define arch_initcall_sync(fn)        __define_initcall(fn, 3s)
#define subsys_initcall(fn)        __define_initcall(fn, 4)
#define subsys_initcall_sync(fn)    __define_initcall(fn, 4s)
#define fs_initcall(fn)            __define_initcall(fn, 5)
#define fs_initcall_sync(fn)        __define_initcall(fn, 5s)
#define rootfs_initcall(fn)        __define_initcall(fn, rootfs)
#define device_initcall(fn)        __define_initcall(fn, 6)
#define device_initcall_sync(fn)    __define_initcall(fn, 6s)
#define late_initcall(fn)        __define_initcall(fn, 7)
#define late_initcall_sync(fn)        __define_initcall(fn, 7s)

在初始化函数调用过后就开进进入主初始化函数，这里对ARM/X86架构进行了区分

static int __init armv8_pmu_driver_init(void)
{if (acpi_disabled)return platform_driver_register(&armv8_pmu_driver);elsereturn arm_pmu_acpi_probe(armv8_pmuv3_init);
}

对于arch=arm64，当然是走的platform_driver_register(&armv8_pmu_driver)，arm架构PMU使用的platform_driver，虚拟platform总线模式，关于platform_driver再额外研究

接下来我们来看armv8_pmu_driver，这里定义出 platform driver所必须的.driver & .probe回调函数，在platform dirver准备就绪后就会以此调用每个driver中的probe？

接着就会调用PMU的通用driver，arm_pmu_device_probe函数定义在driver/perf/arm_pmu_platform.c中

static int armv8_pmu_device_probe(struct platform_device *pdev)
{return arm_pmu_device_probe(pdev, armv8_pmu_of_device_ids, NULL);
}

这里需要说明一下PMU的驱动结构

分为两个大部分

1) 位于driver/perf下的通用driver

2) 与架构相关的，定义在arch/arm64/下的，与指令集相关的，perf_event.c / perf_event_v8.c 等等

arm_pmu_device_probe函数主要做了以下几个事情

pmu = armpmu_alloc();
ret = pmu_parse_irqs(pmu);
ret = init_fn(pmu);
ret = armpmu_request_irqs(pmu);
ret = armpmu_register(pmu);

armpmu_alloc

pmu = kzalloc(sizeof(*pmu), GFP_KERNEL);
pmu->hw_events = alloc_percpu(struct pmu_hw_events);
pmu->pmu = (struct pmu) {.pmu_enable    = armpmu_enable,.pmu_disable   = armpmu_disable,.event_init   = armpmu_event_init,.add       = armpmu_add,.del      = armpmu_del,.start        = armpmu_start,.stop       = armpmu_stop,.read        = armpmu_read,.filter_match    = armpmu_filter_match,.attr_groups = pmu->attr_groups,/** This is a CPU PMU potentially in a heterogeneous* configuration (e.g. big.LITTLE). This is not an uncore PMU,* and we have taken ctx sharing into account (e.g. with our* pmu::filter_match callback and pmu::event_init group* validation).*/.capabilities  = PERF_PMU_CAP_HETEROGENEOUS_CPUS,
};for_each_possible_cpu(cpu) {struct pmu_hw_events *events;events = per_cpu_ptr(pmu->hw_events, cpu);raw_spin_lock_init(&events->pmu_lock);events->percpu_pmu = pmu;
}

这里需要粘贴以下，PMU的结构体

struct arm_pmu {struct pmu   pmu;cpumask_t   active_irqs;cpumask_t   supported_cpus;char     *name;irqreturn_t   (*handle_irq)(int irq_num, void *dev);void      (*enable)(struct perf_event *event);void        (*disable)(struct perf_event *event);int        (*get_event_idx)(struct pmu_hw_events *hw_events,struct perf_event *event);void     (*clear_event_idx)(struct pmu_hw_events *hw_events,struct perf_event *event);int        (*set_event_filter)(struct hw_perf_event *evt,struct perf_event_attr *attr);u32     (*read_counter)(struct perf_event *event);void      (*write_counter)(struct perf_event *event, u32 val);void        (*start)(struct arm_pmu *);void     (*stop)(struct arm_pmu *);void      (*reset)(void *);int        (*map_event)(struct perf_event *event);int      (*filter_match)(struct perf_event *event);int       num_events;u64      max_period;bool     secure_access; /* 32-bit ARM only */
#define ARMV8_PMUV3_MAX_COMMON_EVENTS 0x40DECLARE_BITMAP(pmceid_bitmap, ARMV8_PMUV3_MAX_COMMON_EVENTS);struct platform_device   *plat_device;struct pmu_hw_events   __percpu *hw_events;struct hlist_node   node;struct notifier_block  cpu_pm_nb;/* the attr_groups array must be NULL-terminated */const struct attribute_group *attr_groups[ARMPMU_NR_ATTR_GROUPS + 1];/* Only to be used by ACPI probing code */unsigned long acpi_cpuid;
};

上面填充了该结构体的第一个变量pmu，该结构体定义为：

include/linux/perf_event.h/*** struct pmu - generic performance monitoring unit*/
struct pmu {struct list_head        entry;struct module         *module;struct device           *dev;const struct attribute_group   **attr_groups;const char            *name;int               type;/** various common per-pmu feature flags*/int              capabilities;int * __percpu         pmu_disable_count;struct perf_cpu_context * __percpu pmu_cpu_context;atomic_t           exclusive_cnt; /* < 0: cpu; > 0: tsk */int                task_ctx_nr;int             hrtimer_interval_ms;/* number of address filters this PMU can do */unsigned int         nr_addr_filters;/** Fully disable/enable this PMU, can be used to protect from the PMI* as well as for lazy/batch writing of the MSRs.*/void (*pmu_enable)      (struct pmu *pmu); /* optional */void (*pmu_disable)        (struct pmu *pmu); /* optional *//** Try and initialize the event for this PMU.** Returns:*  -ENOENT    -- @event is not for this PMU**  -ENODEV   -- @event is for this PMU but PMU not present*  -EBUSY -- @event is for this PMU but PMU temporarily unavailable*  -EINVAL    -- @event is for this PMU but @event is not valid*  -EOPNOTSUPP -- @event is for this PMU, @event is valid, but not supported*  -EACCESS    -- @event is for this PMU, @event is valid, but no privilidges**  0       -- @event is for this PMU and valid** Other error return values are allowed.*/int (*event_init)        (struct perf_event *event);/** Notification that the event was mapped or unmapped.  Called* in the context of the mapping task.*/void (*event_mapped)       (struct perf_event *event, struct mm_struct *mm); /* optional */void (*event_unmapped)      (struct perf_event *event, struct mm_struct *mm); /* optional *//** Flags for ->add()/->del()/ ->start()/->stop(). There are* matching hw_perf_event::state flags.*/
#define PERF_EF_START   0x01        /* start the counter when adding    */
#define PERF_EF_RELOAD  0x02        /* reload the counter when starting */
#define PERF_EF_UPDATE  0x04        /* update the counter when stopping *//** Adds/Removes a counter to/from the PMU, can be done inside a* transaction, see the ->*_txn() methods.** The add/del callbacks will reserve all hardware resources required* to service the event, this includes any counter constraint* scheduling etc.** Called with IRQs disabled and the PMU disabled on the CPU the event* is on.** ->add() called without PERF_EF_START should result in the same state*  as ->add() followed by ->stop().** ->del() must always PERF_EF_UPDATE stop an event. If it calls*  ->stop() that must deal with already being stopped without*  PERF_EF_UPDATE.*/int  (*add)         (struct perf_event *event, int flags);void (*del)           (struct perf_event *event, int flags);/** Starts/Stops a counter present on the PMU.** The PMI handler should stop the counter when perf_event_overflow()* returns !0. ->start() will be used to continue.** Also used to change the sample period.** Called with IRQs disabled and the PMU disabled on the CPU the event* is on -- will be called from NMI context with the PMU generates* NMIs.** ->stop() with PERF_EF_UPDATE will read the counter and update*  period/count values like ->read() would.** ->start() with PERF_EF_RELOAD will reprogram the the counter*  value, must be preceded by a ->stop() with PERF_EF_UPDATE.*/void (*start)          (struct perf_event *event, int flags);void (*stop)          (struct perf_event *event, int flags);/** Updates the counter value of the event.** For sampling capable PMUs this will also update the software period* hw_perf_event::period_left field.*/void (*read)            (struct perf_event *event);/** Group events scheduling is treated as a transaction, add* group events as a whole and perform one schedulability test.* If the test fails, roll back the whole group** Start the transaction, after this ->add() doesn't need to* do schedulability tests.** Optional.*/void (*start_txn)        (struct pmu *pmu, unsigned int txn_flags);/** If ->start_txn() disabled the ->add() schedulability test* then ->commit_txn() is required to perform one. On success* the transaction is closed. On error the transaction is kept* open until ->cancel_txn() is called.** Optional.*/int  (*commit_txn)      (struct pmu *pmu);/** Will cancel the transaction, assumes ->del() is called* for each successful ->add() during the transaction.** Optional.*/void (*cancel_txn)     (struct pmu *pmu);/** Will return the value for perf_event_mmap_page::index for this event,* if no implementation is provided it will default to: event->hw.idx + 1.*/int (*event_idx)      (struct perf_event *event); /*optional *//** context-switches callback*/void (*sched_task)      (struct perf_event_context *ctx,bool sched_in);/** PMU specific data size*/size_t               task_ctx_size;/** Set up pmu-private data structures for an AUX area*/void *(*setup_aux)        (int cpu, void **pages,int nr_pages, bool overwrite);/* optional *//** Free pmu-private AUX data structures*/void (*free_aux)       (void *aux); /* optional *//** Validate address range filters: make sure the HW supports the* requested configuration and number of filters; return 0 if the* supplied filters are valid, -errno otherwise.** Runs in the context of the ioctl()ing process and is not serialized* with the rest of the PMU callbacks.*/int (*addr_filters_validate)    (struct list_head *filters);/* optional *//** Synchronize address range filter configuration:* translate hw-agnostic filters into hardware configuration in* event::hw::addr_filters.** Runs as a part of filter sync sequence that is done in ->start()* callback by calling perf_event_addr_filters_sync().** May (and should) traverse event::addr_filters::list, for which its* caller provides necessary serialization.*/void (*addr_filters_sync)  (struct perf_event *event);/* optional *//** Filter events for PMU-specific reasons.*/int (*filter_match)       (struct perf_event *event); /* optional */
};

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