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Message-ID: <20241108204137.2444151-6-howardchu95@gmail.com>
Date: Fri, 8 Nov 2024 12:41:32 -0800
From: Howard Chu <howardchu95@...il.com>
To: acme@...nel.org,
peterz@...radead.org
Cc: namhyung@...nel.org,
irogers@...gle.com,
mingo@...hat.com,
mark.rutland@....com,
james.clark@...aro.org,
alexander.shishkin@...ux.intel.com,
jolsa@...nel.org,
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>
Subject: [PATCH v7 05/10] 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>
---
tools/perf/util/bpf_skel/off_cpu.bpf.c | 83 ++++++++++++++++++++++++--
1 file changed, 78 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 dc6acafb9353..bf652c30b1c9 100644
--- a/tools/perf/util/bpf_skel/off_cpu.bpf.c
+++ b/tools/perf/util/bpf_skel/off_cpu.bpf.c
@@ -18,10 +18,18 @@
#define MAX_STACKS 32
#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 {
@@ -39,6 +47,24 @@ 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));
+ __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_data));
+ __uint(max_entries, 1);
+} offcpu_payload SEC(".maps");
+
struct {
__uint(type, BPF_MAP_TYPE_TASK_STORAGE);
__uint(map_flags, BPF_F_NO_PREALLOC);
@@ -185,6 +211,39 @@ 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;
+}
+
+static int off_cpu_dump(void *ctx, struct offcpu_data *data, struct offcpu_key *key,
+ struct stack *stack, __u64 delta, __u64 timestamp)
+{
+ /* dump tid, period, callchain, and cgroup id */
+ 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)
{
@@ -209,6 +268,12 @@ 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)) {
+ }
+
next:
pelem = bpf_task_storage_get(&tstamp, next, NULL, 0);
@@ -223,11 +288,19 @@ 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) {
+ 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, pelem->timestamp);
+ } 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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