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Message-ID: <20241215181220.754822-5-howardchu95@gmail.com>
Date: Sun, 15 Dec 2024 10:12:14 -0800
From: Howard Chu <howardchu95@...il.com>
To: acme@...nel.org
Cc: namhyung@...nel.org,
mark.rutland@....com,
alexander.shishkin@...ux.intel.com,
jolsa@...nel.org,
irogers@...gle.com,
adrian.hunter@...el.com,
kan.liang@...ux.intel.com,
linux-perf-users@...r.kernel.org,
linux-kernel@...r.kernel.org,
Howard Chu <howardchu95@...il.com>,
Ingo Molnar <mingo@...hat.com>,
James Clark <james.clark@...aro.org>,
Peter Zijlstra <peterz@...radead.org>,
Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: [PATCH v14 04/10] perf record --off-cpu: Dump off-cpu samples in BPF
Collect tid, period, callchain, and cgroup id and dump them when off-cpu
time threshold is reached.
We don't collect the off-cpu time twice (the delta), it's either in
direct samples, or accumulated samples that are dumped at the end of
perf.data.
Suggested-by: Namhyung Kim <namhyung@...nel.org>
Signed-off-by: Howard Chu <howardchu95@...il.com>
Cc: Adrian Hunter <adrian.hunter@...el.com>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Ian Rogers <irogers@...gle.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: James Clark <james.clark@...aro.org>
Cc: Jiri Olsa <jolsa@...nel.org>
Cc: Kan Liang <kan.liang@...ux.intel.com>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Peter Zijlstra <peterz@...radead.org>
Link: https://lore.kernel.org/r/20241108204137.2444151-6-howardchu95@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
tools/perf/util/bpf_skel/off_cpu.bpf.c | 88 ++++++++++++++++++++++++--
1 file changed, 83 insertions(+), 5 deletions(-)
diff --git a/tools/perf/util/bpf_skel/off_cpu.bpf.c b/tools/perf/util/bpf_skel/off_cpu.bpf.c
index 1cdd4d63ea92..77fdc9e81db3 100644
--- a/tools/perf/util/bpf_skel/off_cpu.bpf.c
+++ b/tools/perf/util/bpf_skel/off_cpu.bpf.c
@@ -19,11 +19,17 @@
#define MAX_ENTRIES 102400
#define MAX_CPUS 4096
+#define MAX_OFFCPU_LEN 37
+
+struct stack {
+ u64 array[MAX_STACKS];
+};
struct tstamp_data {
__u32 stack_id;
__u32 state;
__u64 timestamp;
+ struct stack stack;
};
struct offcpu_key {
@@ -41,6 +47,10 @@ struct {
__uint(max_entries, MAX_ENTRIES);
} stacks SEC(".maps");
+struct offcpu_data {
+ u64 array[MAX_OFFCPU_LEN];
+};
+
struct {
__uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
__uint(key_size, sizeof(__u32));
@@ -48,6 +58,13 @@ struct {
__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_data));
+ __uint(max_entries, 1);
+} offcpu_payload SEC(".maps");
+
struct {
__uint(type, BPF_MAP_TYPE_TASK_STORAGE);
__uint(map_flags, BPF_F_NO_PREALLOC);
@@ -106,6 +123,8 @@ const volatile bool uses_cgroup_v1 = false;
int perf_subsys_id = -1;
+__u64 offcpu_thresh_ns = 500000000ull;
+
/*
* 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:
@@ -192,6 +211,47 @@ static inline int can_record(struct task_struct *t, int state)
return 1;
}
+static inline int copy_stack(struct stack *from, struct offcpu_data *to, int n)
+{
+ int len = 0;
+
+ for (int i = 0; i < MAX_STACKS && from->array[i]; ++i, ++len)
+ to->array[n + 2 + i] = from->array[i];
+
+ return len;
+}
+
+/**
+ * off_cpu_dump - dump off-cpu samples to ring buffer
+ * @data: payload for dumping off-cpu samples
+ * @key: off-cpu data
+ * @stack: stack trace of the task before being scheduled out
+ *
+ * If the threshold of off-cpu time is reached, acquire tid, period, callchain, and cgroup id
+ * information of the task, and dump it as a raw sample to perf ring buffer
+ */
+static int off_cpu_dump(void *ctx, struct offcpu_data *data, struct offcpu_key *key,
+ struct stack *stack, __u64 delta)
+{
+ int n = 0, len = 0;
+
+ data->array[n++] = (u64)key->tgid << 32 | key->pid;
+ data->array[n++] = delta;
+
+ /* data->array[n] is callchain->nr (updated later) */
+ data->array[n + 1] = PERF_CONTEXT_USER;
+ data->array[n + 2] = 0;
+ len = copy_stack(stack, data, n);
+
+ /* update length of callchain */
+ data->array[n] = len + 1;
+ n += len + 2;
+
+ data->array[n++] = key->cgroup_id;
+
+ return bpf_perf_event_output(ctx, &offcpu_output, BPF_F_CURRENT_CPU, data, n * sizeof(u64));
+}
+
static int off_cpu_stat(u64 *ctx, struct task_struct *prev,
struct task_struct *next, int state)
{
@@ -216,6 +276,16 @@ static int off_cpu_stat(u64 *ctx, struct task_struct *prev,
pelem->state = state;
pelem->stack_id = stack_id;
+ /*
+ * If stacks are successfully collected by bpf_get_stackid(), collect them once more
+ * in task_storage for direct off-cpu sample dumping
+ */
+ if (stack_id > 0 && bpf_get_stack(ctx, &pelem->stack, MAX_STACKS * sizeof(u64), BPF_F_USER_STACK)) {
+ /*
+ * This empty if block is used to avoid 'result unused warning' from bpf_get_stack().
+ * If the collection fails, continue with the logic for the next task.
+ */
+ }
next:
pelem = bpf_task_storage_get(&tstamp, next, NULL, 0);
@@ -230,11 +300,19 @@ static int off_cpu_stat(u64 *ctx, struct task_struct *prev,
__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);
+ if (delta >= offcpu_thresh_ns) {
+ int zero = 0;
+ struct offcpu_data *data = bpf_map_lookup_elem(&offcpu_payload, &zero);
+
+ if (data)
+ off_cpu_dump(ctx, data, &key, &pelem->stack, delta);
+ } else {
+ total = bpf_map_lookup_elem(&off_cpu, &key);
+ if (total)
+ *total += delta;
+ else
+ bpf_map_update_elem(&off_cpu, &key, &delta, BPF_ANY);
+ }
/* prevent to reuse the timestamp later */
pelem->timestamp = 0;
--
2.43.0
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