Linux内核 eBPF基础：perf（2）：perf性能管理单元PMU的注册
Linux内核 eBPF基础perf（2）：性能管理单元PMU的注册荣涛2021年5月18日
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1. perf类型
在include\uapi\linux\perf_event.h中有：
/*
* attr.type
*/
enum perf_type_id { /* perf 类型 */
PERF_TYPE_HARDWARE = 0, /* 硬件 */
PERF_TYPE_SOFTWARE = 1, /* 软件 */
PERF_TYPE_TRACEPOINT = 2, /* 跟踪点 */
PERF_TYPE_HW_CACHE = 3, /* 硬件cache */
PERF_TYPE_RAW = 4, /* RAW */
PERF_TYPE_BREAKPOINT = 5, /* 断点 */
PERF_TYPE_MAX, /* non-ABI */
};
他们是传入性能管理单元PMU注册函数perf_pmu_register的字段type。列出注册的PMU：
[rongtao@localhost src]$ grep -r "perf_pmu_register" | grep "\""
arch/x86/events/intel/bts.c: return perf_pmu_register(&bts_pmu, "intel_bts", -1);
arch/x86/events/intel/pt.c: ret = perf_pmu_register(&pt_pmu.pmu, "intel_pt", -1);
arch/x86/events/amd/power.c: ret = perf_pmu_register(&pmu_class, "power", -1);
arch/x86/events/core.c: err = perf_pmu_register(&pmu, "cpu", PERF_TYPE_RAW);
arch/x86/events/msr.c: perf_pmu_register(&pmu_msr, "msr", -1);
arch/x86/events/rapl.c: ret = perf_pmu_register(&rapl_pmus->pmu, "power", -1);
kernel/events/hw_breakpoint.c: perf_pmu_register(&perf_breakpoint, "breakpoint", PERF_TYPE_BREAKPOINT);
kernel/events/core.c: perf_pmu_register(&perf_tracepoint, "tracepoint", PERF_TYPE_TRACEPOINT);
kernel/events/core.c: perf_pmu_register(&perf_kprobe, "kprobe", -1);
kernel/events/core.c: perf_pmu_register(&perf_uprobe, "uprobe", -1);
kernel/events/core.c: perf_pmu_register(&perf_swevent, "software", PERF_TYPE_SOFTWARE);
kernel/events/core.c: perf_pmu_register(&perf_cpu_clock, NULL, -1);
kernel/events/core.c: perf_pmu_register(&perf_task_clock, NULL, -1);
2. perf_pmu_register
int perf_pmu_register(struct pmu *pmu, const char *name, int type)
这里需要注意，函数perf_pmu_register是非常重要的注册函数，注册的pmu将加入全局链表pmus中：
static LIST_HEAD(pmus);
函数perf_pmu_register首先申请per-cpu变量：
pmu->pmu_disable_count = alloc_percpu(int);
接着，如果类型不是PERF_TYPE_SOFTWARE，将分配一个ID（前提是name没有设定，如perf_cpu_clock）
if (type != PERF_TYPE_SOFTWARE) {
if (type >= 0)
max = type;
/* 分配一个ID */
ret = idr_alloc(&pmu_idr, pmu, max, 0, GFP_KERNEL);
if (ret < 0)
goto free_pdc;
WARN_ON(type >= 0 && ret != type);
type = ret;
}
然后，申请一个设备：
if (pmu_bus_running/* perf_event_sysfs_init() 中被设置 为 1 */) {
ret = pmu_dev_alloc(pmu); /* 分配一个设备 device- /sys/devices/ */
if (ret)
goto free_idr;
}
接下来这段代码表明，每个hw只能注册一次：
if (pmu->task_ctx_nr == perf_hw_context) {
static int hw_context_taken = 0;
/*
* Other than systems with heterogeneous CPUs, it never makes
* sense for two PMUs to share perf_hw_context. PMUs which are
* uncore must use perf_invalid_context.
*/
if (WARN_ON_ONCE(hw_context_taken &&
!(pmu->capabilities & PERF_PMU_CAP_HETEROGENEOUS_CPUS)))
pmu->task_ctx_nr = perf_invalid_context;
hw_context_taken = 1;
}
否则，其将被设置为perf_invalid_context。然后为每个CPU分配上下文：
pmu->pmu_cpu_context = alloc_percpu(struct perf_cpu_context);
紧接着，进行初始化：
for_each_possible_cpu(cpu) { /* 遍历 CPU */
struct perf_cpu_context *cpuctx;
cpuctx = per_cpu_ptr(pmu->pmu_cpu_context, cpu); /* 1.获取 CPU 的ctx */
__perf_event_init_context(&cpuctx->ctx); /* 2.初始化这个ctx */
lockdep_set_class(&cpuctx->ctx.mutex, &cpuctx_mutex);/*3.初始化lockdep */
lockdep_set_class(&cpuctx->ctx.lock, &cpuctx_lock);
cpuctx->ctx.pmu = pmu; /* 4.指向这个PMU */
cpuctx->online = cpumask_test_cpu(cpu, perf_online_mask);/* 5.是否在线标记 */
__perf_mux_hrtimer_init(cpuctx, cpu); /* 6.高精度定时器，function=perf_mux_hrtimer_handler */
cpuctx->heap_size = ARRAY_SIZE(cpuctx->heap_default);/* */
cpuctx->heap = cpuctx->heap_default; /* 默认使用2个 */
}
其中__perf_event_init_context初始化struct perf_event_context结构：
/*
* Initialize the perf_event context in a task_struct:
*/
static void __perf_event_init_context(struct perf_event_context *ctx) /* 初始化CPU ctx */
{
raw_spin_lock_init(&ctx->lock);
mutex_init(&ctx->mutex);
INIT_LIST_HEAD(&ctx->active_ctx_list);
perf_event_groups_init(&ctx->pinned_groups);
perf_event_groups_init(&ctx->flexible_groups);
INIT_LIST_HEAD(&ctx->event_list);
INIT_LIST_HEAD(&ctx->pinned_active);
INIT_LIST_HEAD(&ctx->flexible_active);
refcount_set(&ctx->refcount, 1);
}
__perf_mux_hrtimer_init初始化一个高精度定时器，
static void __perf_mux_hrtimer_init(struct perf_cpu_context *cpuctx, int cpu) /* 高精度定时器 */
{
struct hrtimer *timer = &cpuctx->hrtimer;
struct pmu *pmu = cpuctx->ctx.pmu;
u64 interval;
/* no multiplexing needed for SW PMU */
if (pmu->task_ctx_nr == perf_sw_context)
return;
/*
* check default is sane, if not set then force to
* default interval (1/tick)
*/
interval = pmu->hrtimer_interval_ms;
if (interval < 1)
interval = pmu->hrtimer_interval_ms = PERF_CPU_HRTIMER; /* 小于1ms，就让他是 1ms */
cpuctx->hrtimer_interval = ns_to_ktime(NSEC_PER_MSEC * interval);
raw_spin_lock_init(&cpuctx->hrtimer_lock);
hrtimer_init(timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED_HARD);
timer->function = perf_mux_hrtimer_handler; /* 处理函数 */
}
需要注意一下几点：
- 如果是软件上下文
perf_sw_context，不创建定时器； - 如果ioctl设置的到期时间小于
1ms，将其设置为1ms； - 会调函数为
perf_mux_hrtimer_handler；
在获取到CPU上下文后，给没有初始化的PMU函数指针赋值：
/* */
if (!pmu->start_txn) {
if (pmu->pmu_enable) {
/*
* If we have pmu_enable/pmu_disable calls, install
* transaction stubs that use that to try and batch
* hardware accesses.
*/
pmu->start_txn = perf_pmu_start_txn;
pmu->commit_txn = perf_pmu_commit_txn;
pmu->cancel_txn = perf_pmu_cancel_txn;
} else {
pmu->start_txn = perf_pmu_nop_txn;
pmu->commit_txn = perf_pmu_nop_int;
pmu->cancel_txn = perf_pmu_nop_void;
}
}
/* 使能 */
if (!pmu->pmu_enable) {
pmu->pmu_enable = perf_pmu_nop_void;
pmu->pmu_disable = perf_pmu_nop_void;
}
/* 检测周期 ioctl(PERF_EVENT_IOC_PERIOD) */
if (!pmu->check_period)
pmu->check_period = perf_event_nop_int;
/* */
if (!pmu->event_idx)
pmu->event_idx = perf_event_idx_default;
下面是将这个PMU添加到pmus链表中：
/*
* Ensure the TYPE_SOFTWARE PMUs are at the head of the list,
* since these cannot be in the IDR. This way the linear search
* is fast, provided a valid software event is provided.
*/
if (type == PERF_TYPE_SOFTWARE || !name)
list_add_rcu(&pmu->entry, &pmus); /* 软件 或者 name=NULL */
else
list_add_tail_rcu(&pmu->entry, &pmus);/* */
需要注意的是，软件类型的PMU将放到链表开头，以提高线性查询速度。
3. 例: software
//kernel/events/core.c
static struct pmu/* 性能监控单元 */ 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,
};
perf_pmu_register(&perf_swevent, "software", PERF_TYPE_SOFTWARE);
3.1. perf_swevent_init
4. 例: perf_cpu_clock
//kernel/events/core.c
static struct pmu perf_cpu_clock = {
.task_ctx_nr = perf_sw_context,
.capabilities = PERF_PMU_CAP_NO_NMI,
.event_init = cpu_clock_event_init,
.add = cpu_clock_event_add,
.del = cpu_clock_event_del,
.start = cpu_clock_event_start,
.stop = cpu_clock_event_stop,
.read = cpu_clock_event_read,
};
perf_pmu_register(&perf_cpu_clock, NULL, -1);
5. 例: perf_task_clock
//kernel/events/core.c
static struct pmu perf_task_clock = {
.task_ctx_nr = perf_sw_context,
.capabilities = PERF_PMU_CAP_NO_NMI,
.event_init = task_clock_event_init,
.add = task_clock_event_add,
.del = task_clock_event_del,
.start = task_clock_event_start,
.stop = task_clock_event_stop,
.read = task_clock_event_read,
};
perf_pmu_register(&perf_task_clock, NULL, -1);
6. 例: kprobe
//kernel/events/core.c
static struct pmu perf_kprobe = {
.task_ctx_nr = perf_sw_context,
.event_init = perf_kprobe_event_init,
.add = perf_trace_add,
.del = perf_trace_del,
.start = perf_swevent_start,
.stop = perf_swevent_stop,
.read = perf_swevent_read,
.attr_groups = kprobe_attr_groups,
};
perf_pmu_register(&perf_kprobe, "kprobe", -1);
7. 例: tracepoint
//kernel/events/core.c
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,
};
perf_pmu_register(&perf_tracepoint, "tracepoint", PERF_TYPE_TRACEPOINT);
8. pmu->event_init
perf_event_alloc
perf_init_event
perf_try_init_event
pmu->event_init(event);
而调用了perf_event_alloc的有：
perf_event_openperf_event_create_kernel_counterfork|clone
kernel_clone
copy_process
perf_event_init_task
perf_event_init_context
inherit_task_group
inherit_group
inherit_event
perf_event_alloc
9. pmu->add
perf_event_enable
_perf_event_enable
__perf_event_enable
ctx_sched_in
ctx_flexible_sched_in|ctx_pinned_sched_in
merge_sched_in
group_sched_in
event_sched_in
event->pmu->add(event, PERF_EF_START)
10. pmu->del
perf_event_disable
_perf_event_disable
__perf_event_disable
group_sched_out
event_sched_out
event->pmu->del(event, 0);
11. pmu->start
12. pmu->stop
13. pmu->read
14. 相关链接
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