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Date: Wed, 18 May 2022 21:02:30 -0700
From: Ian Rogers <irogers@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>,
Jiri Olsa <jolsa@...nel.org>, Ingo Molnar <mingo@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
LKML <linux-kernel@...r.kernel.org>,
Andi Kleen <ak@...ux.intel.com>,
Song Liu <songliubraving@...com>, Hao Luo <haoluo@...gle.com>,
Milian Wolff <milian.wolff@...b.com>, bpf@...r.kernel.org,
linux-perf-users@...r.kernel.org,
Blake Jones <blakejones@...gle.com>
Subject: Re: [PATCH 3/6] perf record: Implement basic filtering for off-cpu
On Wed, May 18, 2022 at 3:47 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> It should honor cpu and task filtering with -a, -C or -p, -t options.
>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
> tools/perf/builtin-record.c | 2 +-
> tools/perf/util/bpf_off_cpu.c | 78 +++++++++++++++++++++++---
> tools/perf/util/bpf_skel/off_cpu.bpf.c | 52 +++++++++++++++--
> tools/perf/util/off_cpu.h | 6 +-
> 4 files changed, 123 insertions(+), 15 deletions(-)
>
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 91f88501412e..7f60d2eac0b4 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -907,7 +907,7 @@ static int record__config_text_poke(struct evlist *evlist)
>
> static int record__config_off_cpu(struct record *rec)
> {
> - return off_cpu_prepare(rec->evlist);
> + return off_cpu_prepare(rec->evlist, &rec->opts.target);
> }
>
> static bool record__kcore_readable(struct machine *machine)
> diff --git a/tools/perf/util/bpf_off_cpu.c b/tools/perf/util/bpf_off_cpu.c
> index 9ed7aca3f4ac..b5e2d038da50 100644
> --- a/tools/perf/util/bpf_off_cpu.c
> +++ b/tools/perf/util/bpf_off_cpu.c
> @@ -6,6 +6,9 @@
> #include "util/off_cpu.h"
> #include "util/perf-hooks.h"
> #include "util/session.h"
> +#include "util/target.h"
> +#include "util/cpumap.h"
> +#include "util/thread_map.h"
> #include <bpf/bpf.h>
>
> #include "bpf_skel/off_cpu.skel.h"
> @@ -60,8 +63,23 @@ static int off_cpu_config(struct evlist *evlist)
> return 0;
> }
>
> -static void off_cpu_start(void *arg __maybe_unused)
> +static void off_cpu_start(void *arg)
> {
> + struct evlist *evlist = arg;
> +
> + /* update task filter for the given workload */
> + if (!skel->bss->has_cpu && !skel->bss->has_task &&
> + perf_thread_map__pid(evlist->core.threads, 0) != -1) {
> + int fd;
> + u32 pid;
> + u8 val = 1;
> +
> + skel->bss->has_task = 1;
> + fd = bpf_map__fd(skel->maps.task_filter);
> + pid = perf_thread_map__pid(evlist->core.threads, 0);
> + bpf_map_update_elem(fd, &pid, &val, BPF_ANY);
> + }
> +
> skel->bss->enabled = 1;
> }
>
> @@ -71,31 +89,75 @@ static void off_cpu_finish(void *arg __maybe_unused)
> off_cpu_bpf__destroy(skel);
> }
>
> -int off_cpu_prepare(struct evlist *evlist)
> +int off_cpu_prepare(struct evlist *evlist, struct target *target)
> {
> - int err;
> + int err, fd, i;
> + int ncpus = 1, ntasks = 1;
>
> if (off_cpu_config(evlist) < 0) {
> pr_err("Failed to config off-cpu BPF event\n");
> return -1;
> }
>
> - set_max_rlimit();
> -
> - skel = off_cpu_bpf__open_and_load();
> + skel = off_cpu_bpf__open();
> if (!skel) {
> pr_err("Failed to open off-cpu BPF skeleton\n");
> return -1;
> }
>
> + /* don't need to set cpu filter for system-wide mode */
> + if (target->cpu_list) {
> + ncpus = perf_cpu_map__nr(evlist->core.user_requested_cpus);
> + bpf_map__set_max_entries(skel->maps.cpu_filter, ncpus);
> + }
> +
> + if (target__has_task(target)) {
> + ntasks = perf_thread_map__nr(evlist->core.threads);
> + bpf_map__set_max_entries(skel->maps.task_filter, ntasks);
> + }
> +
> + set_max_rlimit();
> +
> + err = off_cpu_bpf__load(skel);
> + if (err) {
> + pr_err("Failed to load off-cpu skeleton\n");
> + goto out;
> + }
> +
> + if (target->cpu_list) {
> + u32 cpu;
> + u8 val = 1;
> +
> + skel->bss->has_cpu = 1;
> + fd = bpf_map__fd(skel->maps.cpu_filter);
> +
> + for (i = 0; i < ncpus; i++) {
> + cpu = perf_cpu_map__cpu(evlist->core.user_requested_cpus, i).cpu;
> + bpf_map_update_elem(fd, &cpu, &val, BPF_ANY);
Perhaps more concise with a for_each:
perf_cpu_map__for_each_cpu(cpu, idx, evlist->core.user_requested_cpus)
bpf_map_update_elem(fd, &cpu.cpu, &val, BPF_ANY);
> + }
> + }
> +
> + if (target__has_task(target)) {
> + u32 pid;
> + u8 val = 1;
> +
> + skel->bss->has_task = 1;
> + fd = bpf_map__fd(skel->maps.task_filter);
> +
> + for (i = 0; i < ntasks; i++) {
> + pid = perf_thread_map__pid(evlist->core.threads, i);
> + bpf_map_update_elem(fd, &pid, &val, BPF_ANY);
> + }
> + }
> +
> err = off_cpu_bpf__attach(skel);
> if (err) {
> pr_err("Failed to attach off-cpu BPF skeleton\n");
> goto out;
> }
>
> - if (perf_hooks__set_hook("record_start", off_cpu_start, NULL) ||
> - perf_hooks__set_hook("record_end", off_cpu_finish, NULL)) {
> + if (perf_hooks__set_hook("record_start", off_cpu_start, evlist) ||
> + perf_hooks__set_hook("record_end", off_cpu_finish, evlist)) {
> pr_err("Failed to attach off-cpu skeleton\n");
> goto out;
> }
> diff --git a/tools/perf/util/bpf_skel/off_cpu.bpf.c b/tools/perf/util/bpf_skel/off_cpu.bpf.c
> index 5173ed882fdf..78cdcc8ff863 100644
> --- a/tools/perf/util/bpf_skel/off_cpu.bpf.c
> +++ b/tools/perf/util/bpf_skel/off_cpu.bpf.c
> @@ -49,12 +49,28 @@ struct {
> __uint(max_entries, MAX_ENTRIES);
> } off_cpu 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");
> +
> /* old kernel task_struct definition */
> struct task_struct___old {
> long state;
> } __attribute__((preserve_access_index));
>
> int enabled = 0;
> +int has_cpu = 0;
> +int has_task = 0;
>
> /*
> * Old kernel used to call it task_struct->state and now it's '__state'.
> @@ -74,6 +90,37 @@ static inline int get_task_state(struct task_struct *t)
> return BPF_CORE_READ(t_old, state);
> }
>
> +static inline int can_record(struct task_struct *t, int state)
> +{
> + /* kernel threads don't have user stack */
> + if (t->flags & PF_KTHREAD)
> + return 0;
> +
> + if (state != TASK_INTERRUPTIBLE &&
> + state != TASK_UNINTERRUPTIBLE)
> + return 0;
> +
> + 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 = t->pid;
> +
> + ok = bpf_map_lookup_elem(&task_filter, &pid);
> + if (!ok)
> + return 0;
> + }
> +
> + return 1;
> +}
> +
> SEC("tp_btf/sched_switch")
> int on_switch(u64 *ctx)
> {
> @@ -92,10 +139,7 @@ int on_switch(u64 *ctx)
>
> ts = bpf_ktime_get_ns();
>
> - if (prev->flags & PF_KTHREAD)
> - goto next;
> - if (state != TASK_INTERRUPTIBLE &&
> - state != TASK_UNINTERRUPTIBLE)
> + if (!can_record(prev, state))
> goto next;
>
> stack_id = bpf_get_stackid(ctx, &stacks,
> diff --git a/tools/perf/util/off_cpu.h b/tools/perf/util/off_cpu.h
> index 375d03c424ea..f47af0232e55 100644
> --- a/tools/perf/util/off_cpu.h
> +++ b/tools/perf/util/off_cpu.h
> @@ -2,15 +2,17 @@
> #define PERF_UTIL_OFF_CPU_H
>
> struct evlist;
> +struct target;
> struct perf_session;
>
> #define OFFCPU_EVENT "offcpu-time"
>
> #ifdef HAVE_BPF_SKEL
> -int off_cpu_prepare(struct evlist *evlist);
> +int off_cpu_prepare(struct evlist *evlist, struct target *target);
> int off_cpu_write(struct perf_session *session);
> #else
> -static inline int off_cpu_prepare(struct evlist *evlist __maybe_unused)
> +static inline int off_cpu_prepare(struct evlist *evlist __maybe_unused,
> + struct target *target __maybe_unused)
> {
> return -1;
> }
> --
> 2.36.1.124.g0e6072fb45-goog
>
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