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Message-ID: <Z6uIr8cRZBllFKt4@x1>
Date: Tue, 11 Feb 2025 18:28:15 +0100
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Howard Chu <howardchu95@...il.com>
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, Ingo Molnar <mingo@...hat.com>,
James Clark <james.clark@...aro.org>,
Peter Zijlstra <peterz@...radead.org>,
Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [PATCH v14 04/10] perf record --off-cpu: Dump off-cpu samples in
BPF
On Sun, Dec 15, 2024 at 10:12:14AM -0800, Howard Chu wrote:
> 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];
> +};
So I needed to rename the above as it fails 'make -C tools/perf
build-test', the direct make command line to hit that:
⬢ [acme@...lbox perf-tools-next]$ rm -rf /tmp/build/$(basename $PWD)/ ; mkdir -p /tmp/build/$(basename $PWD)/
⬢ [acme@...lbox perf-tools-next]$ alias m='rm -rf ~/libexec/perf-core/ ; make -k GEN_VMLINUX_H=1 CORESIGHT=1 O=/tmp/build/$(basename $PWD)/ -C tools/perf install-bin && perf test python && cat /tmp/build/perf-tools-next/feature/test-all.output'
⬢ [acme@...lbox perf-tools-next]$ m
GENSKEL /tmp/build/perf-tools-next/util/bpf_skel/sample_filter.skel.h
util/bpf_skel/off_cpu.bpf.c:24:8: error: redefinition of 'stack'
24 | struct stack {
| ^
/tmp/build/perf-tools-next/util/bpf_skel/.tmp/../vmlinux.h:128096:8: note: previous definition is here
128096 | struct stack {
| ^
util/bpf_skel/off_cpu.bpf.c:218:42: error: no member named 'array' in 'struct stack'
218 | for (int i = 0; i < MAX_STACKS && from->array[i]; ++i, ++len)
| ~~~~ ^
util/bpf_skel/off_cpu.bpf.c:219:32: error: no member named 'array' in 'struct stack'
219 | to->array[n + 2 + i] = from->array[i];
| ~~~~ ^
3 errors generated.
make[2]: *** [Makefile.perf:1276: /tmp/build/perf-tools-next/util/bpf_skel/.tmp/off_cpu.bpf.o] Error 1
So for now I'm adding the patch below to get it going.
IIRC there was some discussion about ditching GEN_VMLINUX_H=1, we can
remove this hack later if/when we progress on that.
- Arnaldo
diff --git a/tools/perf/util/bpf_skel/off_cpu.bpf.c b/tools/perf/util/bpf_skel/off_cpu.bpf.c
index 77fdc9e81db395d1..848a123e5610f17b 100644
--- a/tools/perf/util/bpf_skel/off_cpu.bpf.c
+++ b/tools/perf/util/bpf_skel/off_cpu.bpf.c
@@ -21,7 +21,8 @@
#define MAX_CPUS 4096
#define MAX_OFFCPU_LEN 37
-struct stack {
+// We have a 'struct stack' in vmlinux.h when building with GEN_VMLINUX_H=1
+struct __stack {
u64 array[MAX_STACKS];
};
@@ -29,7 +30,7 @@ struct tstamp_data {
__u32 stack_id;
__u32 state;
__u64 timestamp;
- struct stack stack;
+ struct __stack stack;
};
struct offcpu_key {
@@ -211,7 +212,7 @@ 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)
+static inline int copy_stack(struct __stack *from, struct offcpu_data *to, int n)
{
int len = 0;
@@ -231,7 +232,7 @@ static inline int copy_stack(struct stack *from, struct offcpu_data *to, int n)
* 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)
+ struct __stack *stack, __u64 delta)
{
int n = 0, len = 0;
> 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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