Linux内核性能架构：perf_event
Linux内核性能架构：perf_event作者简介：荣涛，csdn博主。组件概述Linux性能子系统在性能分析中非常有用。以下显示了这篇文章中的perf子系统componenet 。“ perf”是可用于执行性能分析的用户程序。仅暴露给用户空间的系统调用perfeventopen返回一个perf事件fd。该系统调用没有glibc包装器。更多信息可以在手册页中阅读。此功能是最复杂的功能之一。“ perf_event”是内核中的核心结构。性能事件有几种类型，例如跟踪点，软件，硬件。我们还可以通过perf event fd将eBPF程序附加到trae事件。抽象层以下显示了perf的抽象层。每个类型的性能事件都有一个对应的PMU（性能监视单元）。例如，跟踪点pmu具有以下pmu。
[*]static struct pmu perf_tracepoint = {
[*].task_ctx_nr = perf_sw_context,
[*].event_init = perf_tp_event_init,
[*].add = perf_trace_add,
[*].del = perf_trace_del,
[*].start = perf_swevent_start,
[*].stop = perf_swevent_stop,
[*].read = perf_swevent_read,
[*]};
与硬件相关的PMU具有与arch-spec有关的抽象结构，例如'struct x86_pmu'。与硬件相关的结构将读取/写入性能监视器MSR。每个PMU都通过调用“ perf_pmu_register”进行注册。性能事件上下文性能可以监视cpu相关事件和任务相关事件。他们两个都可以有几个受监视的事件。因此，我们需要一个上下文来连接事件。这是“ perf_event_context”。有两种上下文，软件和硬件，定义如下：
[*] enum perf_event_task_context {
[*] perf_invalid_context = -1,
[*] perf_hw_context = 0,
[*] perf_sw_context,
[*] perf_nr_task_contexts,
[*] };
对于CPU级别，上下文定义为“ perf_cpu_context”，并在“ struct pmu”中定义为percpu变量。
[*] struct pmu {
[*] ...
[*] struct perf_cpu_context __percpu *pmu_cpu_context;
[*] };
如果PMU是相同类型，则它们将共享一个“ struct perf_cpu_context”。
[*] int perf_pmu_register(struct pmu *pmu, const char *name, int type)
[*] {
[*] int cpu, ret, max = PERF_TYPE_MAX;
[*]
[*] mutex_lock(&pmus_lock);
[*] ...
[*] pmu->pmu_cpu_context = find_pmu_context(pmu->task_ctx_nr);
[*] if (pmu->pmu_cpu_context)
[*] goto got_cpu_context;
[*]
[*] ret = -ENOMEM;
[*] pmu->pmu_cpu_context = alloc_percpu(struct perf_cpu_context);
[*] if (!pmu->pmu_cpu_context)
[*] goto free_dev;
[*]
[*] for_each_possible_cpu(cpu) {
[*] struct perf_cpu_context *cpuctx;
[*]
[*] cpuctx = per_cpu_ptr(pmu->pmu_cpu_context, cpu);
[*] __perf_event_init_context(&cpuctx->ctx);
[*] lockdep_set_class(&cpuctx->ctx.mutex, &cpuctx_mutex);
[*] lockdep_set_class(&cpuctx->ctx.lock, &cpuctx_lock);
[*] cpuctx->ctx.pmu = pmu;
[*] cpuctx->online = cpumask_test_cpu(cpu, perf_online_mask);
[*]
[*] __perf_mux_hrtimer_init(cpuctx, cpu);
[*]
[*] cpuctx->heap_size = ARRAY_SIZE(cpuctx->heap_default);
[*] cpuctx->heap = cpuctx->heap_default;
[*] }
[*]
[*] ...
[*] }
下图显示了此帖子中的相关结构。
对于任务级别，“ task_struct”具有如下定义的指针数组：
[*] struct task_struct {
[*] struct perf_event_context *perf_event_ctxp;
[*] };
下图显示了相关结构，也来自于该帖子。
CPU在线时将触发CPU级性能事件。但是对于任务级别的perf事件，只能通过运行任务来触发它。“ perf_cpu_context”的task_ctx包含当前正在运行的任务的perf上下文。性能事件上下文时间表性能的一项工作是安排任务的perf_event_context的进出时间。下图显示了与性能相关的任务计划输入和输出功能。最后，将调用PMU的add和del回调。让我们以跟踪点为例。add回调是“ perf_trace_add”，而del回调是“ perf_trace_add”。 int perf_trace_add(struct perf_event *p_event, int flags)
[*] {
[*] struct trace_event_call *tp_event = p_event->tp_event;
[*]
[*] if (!(flags & PERF_EF_START))
[*] p_event->hw.state = PERF_HES_STOPPED;
[*]
[*] /*
[*] * If TRACE_REG_PERF_ADD returns false; no custom action was performed
[*] * and we need to take the default action of enqueueing our event on
[*] * the right per-cpu hlist.
[*] */
[*] if (!tp_event->class->reg(tp_event, TRACE_REG_PERF_ADD, p_event)) {
[*] struct hlist_head __percpu *pcpu_list;
[*] struct hlist_head *list;
[*]
[*] pcpu_list = tp_event->perf_events;
[*] if (WARN_ON_ONCE(!pcpu_list))
[*] return -EINVAL;
[*]
[*] list = this_cpu_ptr(pcpu_list);
[*] hlist_add_head_rcu(&p_event->hlist_entry, list);
[*] }
[*]
[*] return 0;
[*] }
[*]
[*] void perf_trace_del(struct perf_event *p_event, int flags)
[*] {
[*] struct trace_event_call *tp_event = p_event->tp_event;
[*]
[*] /*
[*] * If TRACE_REG_PERF_DEL returns false; no custom action was performed
[*] * and we need to take the default action of dequeueing our event from
[*] * the right per-cpu hlist.
[*] */
[*] if (!tp_event->class->reg(tp_event, TRACE_REG_PERF_DEL, p_event))
[*] hlist_del_rcu(&p_event->hlist_entry);
[*] }
“ perf_event”将被添加或删除到“ tp_event-> perf_events”列表中。perf_event_open流
[*] perf_event_open
[*] ->perf_copy_attr
[*] ->get_unused_fd_flags(fd)
[*] ->perf_event_alloc
[*] ->perf_init_event
[*] ->perf_try_init_event
[*] ->pmu->event_init()
[*] ->find_get_context
[*] ->perf_install_in_context
[*] ->__perf_install_in_context
[*] ->add_event_to_ctx
[*] ->list_add_event
[*] ->perf_group_attach
[*] ->add_event_to_ctx
[*] ->fd_install
perf_event_open将调用'pmu-> event_init'来初始化事件。并将perf_event添加到perf_event_context中。性能跟踪事件回顾跟踪点PMU的定义。
[*] static struct pmu perf_tracepoint = {
[*] .task_ctx_nr = perf_sw_context,
[*]
[*] .event_init = perf_tp_event_init,
[*] .add = perf_trace_add,
[*] .del = perf_trace_del,
[*] .start = perf_swevent_start,
[*] .stop = perf_swevent_stop,
[*] .read = perf_swevent_read,
[*] };
让我们尝试看一下perf子系统如何监视跟踪点事件。性能事件初始化称为“ perf_tp_event_init”。
[*]perf_tp_event_init
[*] ->perf_trace_init
[*] ->perf_trace_event_init
[*] ->perf_trace_event_reg
[*] ->tp_event->class->reg(TRACE_REG_PERF_REGISTER)
'perf_trace_init'将找到指定的跟踪点。“ perf_trace_event_reg”将分配并初始化“ tp_event_perf_events”列表。并使用TRACE_REG_PERF_REGISTER调用“ tp_event-> class-> reg”。
[*]static int perf_trace_event_reg(struct trace_event_call *tp_event,
[*] struct perf_event *p_event)
[*]{
[*] struct hlist_head __percpu *list;
[*] int ret = -ENOMEM;
[*] int cpu;
[*]
[*] p_event->tp_event = tp_event;
[*] if (tp_event->perf_refcount++ > 0)
[*] return 0;
[*]
[*] list = alloc_percpu(struct hlist_head);
[*] if (!list)
[*] goto fail;
[*]
[*] for_each_possible_cpu(cpu)
[*] INIT_HLIST_HEAD(per_cpu_ptr(list, cpu));
[*]
[*] tp_event->perf_events = list;
[*]
[*] ...
[*] ret = tp_event->class->reg(tp_event, TRACE_REG_PERF_REGISTER, NULL);
[*] if (ret)
[*] goto fail;
[*]
[*] total_ref_count++;
[*] return 0;
[*] ...
[*]}
“ tp_event_> class-> reg”回调为“ trace_event_reg”。
[*] int trace_event_reg(struct trace_event_call *call,
[*] enum trace_reg type, void *data)
[*] {
[*] struct trace_event_file *file = data;
[*]
[*] WARN_ON(!(call->flags & TRACE_EVENT_FL_TRACEPOINT));
[*] switch (type) {
[*] ...
[*]
[*] #ifdef CONFIG_PERF_EVENTS
[*] case TRACE_REG_PERF_REGISTER:
[*] return tracepoint_probe_register(call->tp,
[*] call->class->perf_probe,
[*] call);
[*] case TRACE_REG_PERF_UNREGISTER:
[*] tracepoint_probe_unregister(call->tp,
[*] call->class->perf_probe,
[*] call);
[*] return 0;
[*] case TRACE_REG_PERF_OPEN:
[*] case TRACE_REG_PERF_CLOSE:
[*] case TRACE_REG_PERF_ADD:
[*] case TRACE_REG_PERF_DEL:
[*] return 0;
[*] #endif
[*] }
[*] return 0;
[*] }
我们可以看到'call-> class-> perf_probe'将被注册到跟踪点。从我的帖子。我们知道这个“ perf_probe”是“ perf_trace _ ## call”。
[*]static notrace void
[*] perf_trace_##call(void *__data, proto)
[*] {
[*] struct trace_event_call *event_call = __data;
[*] struct trace_event_data_offsets_##call __maybe_unused __data_offsets;
[*] struct trace_event_raw_##call *entry;
[*] struct pt_regs *__regs;
[*] u64 __count = 1;
[*] struct task_struct *__task = NULL;
[*] struct hlist_head *head; int __entry_size;
[*] int __data_size;
[*] int rctx;
[*]
[*] __data_size = trace_event_get_offsets_##call(&__data_offsets, args);
[*]
[*] head = this_cpu_ptr(event_call->perf_events);
[*] if (!bpf_prog_array_valid(event_call) &&
[*] __builtin_constant_p(!__task) && !__task &&
[*] hlist_empty(head)) return;
[*]
[*] __entry_size = ALIGN(__data_size + sizeof(*entry) + sizeof(u32),
[*] sizeof(u64));
[*] __entry_size -= sizeof(u32);
[*]
[*] entry = perf_trace_buf_alloc(__entry_size, &__regs, &rctx);
[*] if (!entry)
[*] return;
[*]
[*] perf_fetch_caller_regs(__regs);
[*]
[*] tstruct
[*]
[*] { assign; }
[*]
[*] perf_trace_run_bpf_submit(entry, __entry_size, rctx,
[*] event_call, __count, __regs,
[*] head, __task);
[*] }
如果“ event_call-> perf_events”为空，则表示没有任何当前的perf_event添加到该跟踪点。这是'perf_event_open'初始化perf_event时的默认状态。性能事件添加在CPU中调度任务时，将调用'pmu-> add'，并将'perf_event'链接到'event_call-> perf_events'链接列表。性能事件从CPU调度任务后，将调用“ pmu-> del”，并且将从“ event_call-> perf_events”链接列表中删除“ perf_event”。性能事件触发器如果'event_call-> perf_events'不为空，则将调用'perf_trace_run_bpf_submit'。如果没有附加eBPF程序，则将调用“ perf_tp_event”。
[*] void perf_tp_event(u16 event_type, u64 count,
[*]void *record, int entry_size,
[*] struct pt_regs *regs, struct hlist_head *head, int rctx,
[*] struct task_struct *task)
[*] {
[*] struct perf_sample_data data;
[*] struct perf_event *event;
[*]
[*] struct perf_raw_record raw = {
[*] .frag = {
[*] .size = entry_size,
[*] .data = record,
[*] },
[*] };
[*]
[*] perf_sample_data_init(&data, 0, 0);
[*] data.raw = &raw;
[*]
[*] perf_trace_buf_update(record, event_type);
[*]
[*] hlist_for_each_entry_rcu(event, head, hlist_entry) {
[*] if (perf_tp_event_match(event, &data, regs))
[*] perf_swevent_event(event, count, &data, regs);
[*] }
[*]
[*] ...
[*] perf_swevent_put_recursion_context(rctx);
[*] }
对于“ event_call-> perf_events”列表中的每个“ perf_event”。它调用perf_swevent_event触发性能事件。
[*] static void perf_swevent_event(struct perf_event *event,
[*] u64 nr,struct perf_sample_data *data,
[*] struct pt_regs *regs)
[*] {
[*] struct hw_perf_event *hwc = &event->hw;
[*]
[*] local64_add(nr, &event->count);
[*]
[*] if (!regs)
[*] return;
[*]
[*] if (!is_sampling_event(event))
[*] return;
[*]
[*] if ((event->attr.sample_type & PERF_SAMPLE_PERIOD)
[*] && !event->attr.freq) {
[*] data->period = nr;
[*] return perf_swevent_overflow(event, 1, data, regs);
[*] } else
[*] data->period = event->hw.last_period;
[*]
[*] if (nr == 1 && hwc->sample_period == 1 &&
[*] !event->attr.freq)
[*] return perf_swevent_overflow(event, 1, data, regs);
[*]
[*] if (local64_add_negative(nr, &hwc->period_left))
[*] return;
[*]
[*] perf_swevent_overflow(event, 0, data, regs);
[*] }
[*] static void perf_swevent_event(struct perf_event *event,
[*] u64 nr,struct perf_sample_data *data,
[*] struct pt_regs *regs)
[*] {
[*] struct hw_perf_event *hwc = &event->hw;
[*]
[*] local64_add(nr, &event->count);
[*]
[*] if (!regs)
[*] return;
[*]
[*] if (!is_sampling_event(event))
[*] return;
[*]
[*] if ((event->attr.sample_type & PERF_SAMPLE_PERIOD)
[*] && !event->attr.freq) {
[*] data->period = nr;
[*] return perf_swevent_overflow(event, 1, data, regs);
[*] } else
[*] data->period = event->hw.last_period;
[*]
[*] if (nr == 1 && hwc->sample_period == 1
[*] && !event->attr.freq)
[*] return perf_swevent_overflow(event, 1, data, regs);
[*]
[*] if (local64_add_negative(nr, &hwc->period_left))
[*] return;
[*]
[*] perf_swevent_overflow(event, 0, data, regs);
[*] }
'perf_swevent_event'添加'event-> count'。如果事件未采样，则仅返回。Tis是性能计数模式。如果perf_event在样本模式下，则需要复制跟踪点数据。以下是呼叫链。
[*]perf_swevent_overflow
[*] ->__perf_event_overflow->event
[*] ->overflow_handler(perf_event_output).
软件性能事件软件PMU定义如下：
[*] static struct pmu perf_swevent = {
[*] .task_ctx_nr = perf_sw_context,
[*]
[*] .capabilities = PERF_PMU_CAP_NO_NMI,
[*]
[*] .event_init = perf_swevent_init,
[*] .add = perf_swevent_add,
[*] .del = perf_swevent_del,
[*] .start = perf_swevent_start,
[*] .stop = perf_swevent_stop,
[*] .read = perf_swevent_read,
[*] };
性能事件初始化“ perf_swevent_init”将被调用。它称为“ swevent_hlist_get”
[*] static int perf_swevent_init(struct perf_event *event)
[*] {
[*] u64 event_id = event->attr.config;
[*]
[*] if (event->attr.type != PERF_TYPE_SOFTWARE)
[*] return -ENOENT;
[*]
[*] /*
[*] * no branch sampling for software events
[*] */
[*] if (has_branch_stack(event))
[*] return -EOPNOTSUPP;
[*]
[*] switch (event_id) {
[*] case PERF_COUNT_SW_CPU_CLOCK:
[*] case PERF_COUNT_SW_TASK_CLOCK:
[*] return -ENOENT;
[*]
[*] default:
[*] break;
[*] }
[*]
[*] if (event_id >= PERF_COUNT_SW_MAX)
[*] return -ENOENT;
[*]
[*] if (!event->parent) {
[*] int err;
[*]
[*] err = swevent_hlist_get();
[*] if (err)
[*] return err;
[*]
[*] static_key_slow_inc(&perf_swevent_enabled);
[*] event->destroy = sw_perf_event_destroy;
[*] }
[*]
[*] return 0;
[*] }
这将创建一个percpu'swhash-> swevent_hlist'列表。还要将perf_swevent_enabled 设置为true。性能事件添加'perf_swevent_add'将perf_event添加到percpu哈希列表中。
[*] static int perf_swevent_add(struct perf_event *event, int flags)
[*] {
[*] struct swevent_htable *swhash = this_cpu_ptr(&swevent_htable);
[*] struct hw_perf_event *hwc = &event->hw;
[*] struct hlist_head *head;
[*]
[*] if (is_sampling_event(event)) {
[*] hwc->last_period = hwc->sample_period;
[*] perf_swevent_set_period(event);
[*] }
[*]
[*] hwc->state = !(flags & PERF_EF_START);
[*]
[*] head = find_swevent_head(swhash, event);
[*] if (WARN_ON_ONCE(!head))
[*] return -EINVAL;
[*]
[*] hlist_add_head_rcu(&event->hlist_entry, head);
[*] perf_event_update_userpage(event);
[*]
[*] return 0;
[*] }
性能事件'perf_swevent_del'从哈希列表中删除。
[*] static void perf_swevent_del(struct perf_event *event, int flags)
[*] {
[*] hlist_del_rcu(&event->hlist_entry);
[*] }
[*]
性能事件触发器以任务开关为例。“ perf_sw_event_sched”将被调用。
[*] static inline void perf_event_task_sched_out(struct task_struct *prev,
[*] struct task_struct *next)
[*] {
[*] perf_sw_event_sched(PERF_COUNT_SW_CONTEXT_SWITCHES, 1, 0);
[*]
[*] if (static_branch_unlikely(&perf_sched_events))
[*] __perf_event_task_sched_out(prev, next);
[*] }
在perf_event_task_sched_out-> _perf_sw_event-> do_perf_sw_event调用链之后。
[*] static void do_perf_sw_event(enum perf_type_id type, u32 event_id,
[*] u64 nr,
[*] struct perf_sample_data *data,
[*] struct pt_regs *regs)
[*] {
[*] struct swevent_htable *swhash = this_cpu_ptr(&swevent_htable);
[*] struct perf_event *event;
[*] struct hlist_head *head;
[*]
[*] rcu_read_lock();
[*] head = find_swevent_head_rcu(swhash, type, event_id);
[*] if (!head)
[*] goto end;
[*]
[*] hlist_for_each_entry_rcu(event, head, hlist_entry) {
[*] if (perf_swevent_match(event, type, event_id, data, regs))
[*] perf_swevent_event(event, nr, data, regs);
[*] }
[*] end:
[*] rcu_read_unlock();
[*] }
如我们所见，它最终会调用“ perf_swevent_event”来触发事件。硬件性能事件硬件PMU之一定义如下：
[*] static struct pmu pmu = {
[*] .pmu_enable = x86_pmu_enable,
[*] .pmu_disable = x86_pmu_disable,
[*]
[*] .attr_groups = x86_pmu_attr_groups,
[*]
[*] .event_init = x86_pmu_event_init,
[*]
[*] .event_mapped = x86_pmu_event_mapped,
[*] .event_unmapped = x86_pmu_event_unmapped,
[*]
[*] .add = x86_pmu_add,
[*] .del = x86_pmu_del,
[*] .start = x86_pmu_start,
[*] .stop = x86_pmu_stop,
[*] .read = x86_pmu_read,
[*]
[*] .start_txn = x86_pmu_start_txn,
[*] .cancel_txn = x86_pmu_cancel_txn,
[*] .commit_txn = x86_pmu_commit_txn,
[*]
[*] .event_idx = x86_pmu_event_idx,
[*] .sched_task = x86_pmu_sched_task,
[*] .task_ctx_size = sizeof(struct x86_perf_task_context),
[*] .swap_task_ctx = x86_pmu_swap_task_ctx,
[*] .check_period = x86_pmu_check_period,
[*]
[*] .aux_output_match = x86_pmu_aux_output_match,
[*] };
硬件性能事件非常复杂，因为它将与硬件交互。这里不会深入介绍硬件。性能事件初始化
[*] x86_pmu_event_init
[*] ->__x86_pmu_event_init
[*] ->x86_reserve_hardware
[*] ->x86_pmu.hw_config()
[*] ->validate_event
此处的“ x86_pmu”是基于arch规范的PMU结构。性能事件添加x86_pmu_add->收集事件->-> x86_pmu.schedule_events（）-> x86_pmu.add'collect_events'集
[*] cpuc->event_list = leader;
性能事件x86_pmu_del将删除“ cpuc-> event_list”中的事件。性能事件触发器触发硬件事件时，它将触发NMI中断。此处理程序是“ perf_event_nmi_handler”。
[*] static int
[*] perf_event_nmi_handler(unsigned int cmd, struct pt_regs *regs)
[*] {
[*] u64 start_clock;
[*] u64 finish_clock;
[*] int ret;
[*]
[*] /*
[*] * All PMUs/events that share this PMI handler should make sure to
[*] * increment active_events for their events.
[*] */
[*] if (!atomic_read(&active_events))
[*] return NMI_DONE;
[*]
[*] start_clock = sched_clock();
[*] ret = x86_pmu.handle_irq(regs);
[*] finish_clock = sched_clock();
[*]
[*] perf_sample_event_took(finish_clock - start_clock);
[*]
[*] return ret;
[*] }
以Taks'x86_pmu.handle_irq'= x86_pmu_handle_irq为例。
[*] for (idx = 0; idx < x86_pmu.num_counters; idx++) {
[*] if (!test_bit(idx, cpuc->active_mask))
[*] continue;
[*]
[*] event = cpuc->events;
[*]
[*] val = x86_perf_event_update(event);
[*] if (val & (1ULL << (x86_pmu.cntval_bits - 1)))
[*] continue;
[*]
[*] /*
[*] * event overflow
[*] */
[*] handled++;
[*] perf_sample_data_init(&data, 0, event->hw.last_period);
[*]
[*] if (!x86_perf_event_set_period(event))
[*] continue;
[*]
[*] if (perf_event_overflow(event, &data, regs))
[*] x86_pmu_stop(event, 0);
[*] }
[*]
在这里，我们可以看到它对“ cpuc”进行了迭代，以查找触发该中断的事件。参考资料：Linux kernel perf architecture (terenceli.github.io)
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