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// SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
// Copyright (c) 2022 Google
#include "vmlinux.h"
#include <bpf/bpf_helpers.h>
#include <bpf/bpf_tracing.h>
#include <bpf/bpf_core_read.h>
/* maximum stack trace depth */
#define MAX_STACKS 8
/* default buffer size */
#define MAX_ENTRIES 10240
struct contention_key {
__s32 stack_id;
};
struct contention_data {
__u64 total_time;
__u64 min_time;
__u64 max_time;
__u32 count;
__u32 flags;
};
struct tstamp_data {
__u64 timestamp;
__u64 lock;
__u32 flags;
__s32 stack_id;
};
/* callstack storage */
struct {
__uint(type, BPF_MAP_TYPE_STACK_TRACE);
__uint(key_size, sizeof(__u32));
__uint(value_size, MAX_STACKS * sizeof(__u64));
__uint(max_entries, MAX_ENTRIES);
} stacks SEC(".maps");
/* maintain timestamp at the beginning of contention */
struct {
__uint(type, BPF_MAP_TYPE_TASK_STORAGE);
__uint(map_flags, BPF_F_NO_PREALLOC);
__type(key, int);
__type(value, struct tstamp_data);
} tstamp SEC(".maps");
/* actual lock contention statistics */
struct {
__uint(type, BPF_MAP_TYPE_HASH);
__uint(key_size, sizeof(struct contention_key));
__uint(value_size, sizeof(struct contention_data));
__uint(max_entries, MAX_ENTRIES);
} lock_stat SEC(".maps");
struct {
__uint(type, BPF_MAP_TYPE_HASH);
__uint(key_size, sizeof(__u32));
__uint(value_size, sizeof(__u8));
__uint(max_entries, 1);
} cpu_filter SEC(".maps");
struct {
__uint(type, BPF_MAP_TYPE_HASH);
__uint(key_size, sizeof(__u32));
__uint(value_size, sizeof(__u8));
__uint(max_entries, 1);
} task_filter SEC(".maps");
/* control flags */
int enabled;
int has_cpu;
int has_task;
int stack_skip;
/* error stat */
unsigned long lost;
static inline int can_record(void)
{
if (has_cpu) {
__u32 cpu = bpf_get_smp_processor_id();
__u8 *ok;
ok = bpf_map_lookup_elem(&cpu_filter, &cpu);
if (!ok)
return 0;
}
if (has_task) {
__u8 *ok;
__u32 pid = bpf_get_current_pid_tgid();
ok = bpf_map_lookup_elem(&task_filter, &pid);
if (!ok)
return 0;
}
return 1;
}
SEC("tp_btf/contention_begin")
int contention_begin(u64 *ctx)
{
struct task_struct *curr;
struct tstamp_data *pelem;
if (!enabled || !can_record())
return 0;
curr = bpf_get_current_task_btf();
pelem = bpf_task_storage_get(&tstamp, curr, NULL,
BPF_LOCAL_STORAGE_GET_F_CREATE);
if (!pelem || pelem->lock)
return 0;
pelem->timestamp = bpf_ktime_get_ns();
pelem->lock = (__u64)ctx[0];
pelem->flags = (__u32)ctx[1];
pelem->stack_id = bpf_get_stackid(ctx, &stacks, BPF_F_FAST_STACK_CMP | stack_skip);
if (pelem->stack_id < 0)
lost++;
return 0;
}
SEC("tp_btf/contention_end")
int contention_end(u64 *ctx)
{
struct task_struct *curr;
struct tstamp_data *pelem;
struct contention_key key;
struct contention_data *data;
__u64 duration;
if (!enabled)
return 0;
curr = bpf_get_current_task_btf();
pelem = bpf_task_storage_get(&tstamp, curr, NULL, 0);
if (!pelem || pelem->lock != ctx[0])
return 0;
duration = bpf_ktime_get_ns() - pelem->timestamp;
key.stack_id = pelem->stack_id;
data = bpf_map_lookup_elem(&lock_stat, &key);
if (!data) {
struct contention_data first = {
.total_time = duration,
.max_time = duration,
.min_time = duration,
.count = 1,
.flags = pelem->flags,
};
bpf_map_update_elem(&lock_stat, &key, &first, BPF_NOEXIST);
pelem->lock = 0;
return 0;
}
__sync_fetch_and_add(&data->total_time, duration);
__sync_fetch_and_add(&data->count, 1);
/* FIXME: need atomic operations */
if (data->max_time < duration)
data->max_time = duration;
if (data->min_time > duration)
data->min_time = duration;
pelem->lock = 0;
return 0;
}
char LICENSE[] SEC("license") = "Dual BSD/GPL";
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