bpf_perf_event_output the off-cpu samples on sched_switch. Because most of
the time can_record() returns 0, we can't collect stacks, so when stack
trace is collectable, store it in stack_save for later output. If we
don't do that, most of the off-cpu samples won't have a stack trace.
And since stack traces are collected in task_storage, we don't need to
worry about maps getting data overflow.
There is a threshold OUTPUT_THRESHOLD (ns) to decide the minimum off-CPU
time to trigger output, it is now set to zero. I need opinions on this
value.
Signed-off-by: Howard Chu <howardchu95@xxxxxxxxx>
---
tools/perf/util/bpf_skel/off_cpu.bpf.c | 163 ++++++++++++++++++++-----
1 file changed, 135 insertions(+), 28 deletions(-)
diff --git a/tools/perf/util/bpf_skel/off_cpu.bpf.c b/tools/perf/util/bpf_skel/off_cpu.bpf.c
index d877a0a9731f..81114de2436d 100644
--- a/tools/perf/util/bpf_skel/off_cpu.bpf.c
+++ b/tools/perf/util/bpf_skel/off_cpu.bpf.c
@@ -17,9 +17,13 @@
#define MAX_STACKS 32
#define MAX_ENTRIES 102400
+#define MAX_CPUS 4096
+#define MAX_OFFCPU_LEN 128
+
+/* minimum offcpu time to trigger output */
+#define OUTPUT_THRESHOLD 0ULL
struct tstamp_data {
- __u32 stack_id;
__u32 state;
__u64 timestamp;
};
@@ -27,17 +31,17 @@ struct tstamp_data {
struct offcpu_key {
__u32 pid;
__u32 tgid;
- __u32 stack_id;
__u32 state;
__u64 cgroup_id;
};
-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");
+struct offcpu_array {
+ u64 array[MAX_OFFCPU_LEN];
+};
+
+struct stack_array {
+ u64 array[MAX_STACKS];
+};
struct {
__uint(type, BPF_MAP_TYPE_TASK_STORAGE);
@@ -46,13 +50,6 @@ struct {
__type(value, struct tstamp_data);
} tstamp SEC(".maps");
-struct {
- __uint(type, BPF_MAP_TYPE_HASH);
- __uint(key_size, sizeof(struct offcpu_key));
- __uint(value_size, sizeof(__u64));
- __uint(max_entries, MAX_ENTRIES);
-} off_cpu SEC(".maps");
-
struct {
__uint(type, BPF_MAP_TYPE_HASH);
__uint(key_size, sizeof(__u32));
@@ -74,6 +71,34 @@ struct {
__uint(max_entries, 1);
} cgroup_filter SEC(".maps");
+struct {
+ __uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
+ __uint(key_size, sizeof(__u32));
+ __uint(value_size, sizeof(__u32));
+ __uint(max_entries, MAX_CPUS);
+} offcpu_output SEC(".maps");
+
+struct {
+ __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
+ __uint(key_size, sizeof(__u32));
+ __uint(value_size, sizeof(struct offcpu_array));
+ __uint(max_entries, 1);
+} offcpu_data SEC(".maps");
+
+struct {
+ __uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
+ __uint(key_size, sizeof(__u32));
+ __uint(value_size, sizeof(struct stack_array));
+ __uint(max_entries, 1);
+} stack_frame SEC(".maps");
+
+struct {
+ __uint(type, BPF_MAP_TYPE_TASK_STORAGE);
+ __uint(map_flags, BPF_F_NO_PREALLOC);
+ __type(key, int);
+ __type(value, struct stack_array);
+} stack_save SEC(".maps");
+
/* new kernel task_struct definition */
struct task_struct___new {
long __state;
@@ -96,6 +121,8 @@ const volatile bool uses_cgroup_v1 = false;
int perf_subsys_id = -1;
+u64 sample_id, sample_type;
+
/*
* Old kernel used to call it task_struct->state and now it's '__state'.
* Use BPF CO-RE "ignored suffix rule" to deal with it like below:
@@ -182,50 +209,130 @@ static inline int can_record(struct task_struct *t, int state)
return 1;
}
+static inline bool check_bounds(int index)
+{
+ if (index >= 0 && index < MAX_OFFCPU_LEN)
+ return true;
+
+ return false;
+}
+
+static inline int copy_stack(struct stack_array *from,
+ struct offcpu_array *to, int n)
+{
+ int max_stacks = MAX_STACKS, len = 0;
+
+ if (!from)
+ return len;
+
+ for (int i = 0; i < max_stacks && from->array[i]; ++i) {
+ if (check_bounds(n + 2 + i)) {
+ to->array[n + 2 + i] = from->array[i];
+ ++len;
+ }
+ }
+ return len;
+}
+
static int off_cpu_stat(u64 *ctx, struct task_struct *prev,
struct task_struct *next, int state)
{
__u64 ts;
- __u32 stack_id;
struct tstamp_data *pelem;
-
+ struct stack_array *frame, *stack_save_p;
ts = bpf_ktime_get_ns();
+ int zero = 0, len = 0, size;
if (!can_record(prev, state))
goto next;
- stack_id = bpf_get_stackid(ctx, &stacks,
- BPF_F_FAST_STACK_CMP | BPF_F_USER_STACK);
+ frame = bpf_map_lookup_elem(&stack_frame, &zero);
+ if (frame)
+ len = bpf_get_stack(ctx, frame->array, MAX_STACKS * sizeof(u64),
+ BPF_F_USER_STACK) / sizeof(u64);
+
+ /* save stacks if collectable */
+ if (len > 0) {
+ stack_save_p = bpf_task_storage_get(&stack_save, prev, NULL,
+ BPF_LOCAL_STORAGE_GET_F_CREATE);
+ if (stack_save_p)
+ for (int i = 0; i < len && i < MAX_STACKS; ++i)
+ stack_save_p->array[i] = frame->array[i];
+ }
pelem = bpf_task_storage_get(&tstamp, prev, NULL,
BPF_LOCAL_STORAGE_GET_F_CREATE);
+
if (!pelem)
goto next;
pelem->timestamp = ts;
pelem->state = state;
- pelem->stack_id = stack_id;
next:
pelem = bpf_task_storage_get(&tstamp, next, NULL, 0);
+ stack_save_p = bpf_task_storage_get(&stack_save, next, NULL, 0);
+
if (pelem && pelem->timestamp) {
struct offcpu_key key = {
.pid = next->pid,
.tgid = next->tgid,
- .stack_id = pelem->stack_id,
.state = pelem->state,
.cgroup_id = needs_cgroup ? get_cgroup_id(next) : 0,
};
- __u64 delta = ts - pelem->timestamp;
- __u64 *total;
- total = bpf_map_lookup_elem(&off_cpu, &key);
- if (total)
- *total += delta;
- else
- bpf_map_update_elem(&off_cpu, &key, &delta, BPF_ANY);
+ __u64 delta = ts - pelem->timestamp;
+ struct offcpu_array *data = bpf_map_lookup_elem(&offcpu_data, &zero);
+
+ if (data && delta >= OUTPUT_THRESHOLD) {
+ int n = 0;
+ int ip_pos = -1;
+
+ if (sample_type & PERF_SAMPLE_IDENTIFIER && check_bounds(n))
+ data->array[n++] = sample_id;
+ if (sample_type & PERF_SAMPLE_IP && check_bounds(n)) {
+ ip_pos = n;
+ data->array[n++] = 0; /* will be updated */
+ }
+ if (sample_type & PERF_SAMPLE_TID && check_bounds(n))
+ data->array[n++] = (u64)key.pid << 32 | key.tgid;
+ if (sample_type & PERF_SAMPLE_TIME && check_bounds(n))
+ data->array[n++] = pelem->timestamp;
+ if (sample_type & PERF_SAMPLE_ID && check_bounds(n))
+ data->array[n++] = sample_id;
+ if (sample_type & PERF_SAMPLE_CPU && check_bounds(n))
+ data->array[n++] = 0;
+ if (sample_type & PERF_SAMPLE_PERIOD && check_bounds(n))
+ data->array[n++] = delta;
+ if (sample_type & PERF_SAMPLE_CALLCHAIN && check_bounds(n + 2)) {
+ len = 0;
+
+ /* data->array[n] is callchain->nr (updated later) */
+ data->array[n + 1] = PERF_CONTEXT_USER;
+ data->array[n + 2] = 0;
+
+ len = copy_stack(stack_save_p, data, n);
+
+ /* update length of callchain */
+ data->array[n] = len + 1;
+
+ /* update sample ip with the first callchain entry */
+ if (ip_pos >= 0)
+ data->array[ip_pos] = data->array[n + 2];
+
+ /* calculate sample callchain data->array length */
+ n += len + 2;
+ }
+ if (sample_type & PERF_SAMPLE_CGROUP && check_bounds(n))
+ data->array[n++] = key.cgroup_id;
+
+ size = n * sizeof(u64);
+ if (size >= 0 && size <= MAX_OFFCPU_LEN * sizeof(u64))
+ bpf_perf_event_output(ctx, &offcpu_output, BPF_F_CURRENT_CPU,
+ data, size);
+ }
/* prevent to reuse the timestamp later */
pelem->timestamp = 0;
}
--
2.44.0
