perf lock contention: Constify control data for BPF

The control knobs set before loading BPF programs should be declared as
'const volatile' so that it can be optimized by the BPF core.

Committer testing:

  root@x1:~# perf lock contention --use-bpf
   contended   total wait     max wait     avg wait         type   caller

           5     31.57 us     14.93 us      6.31 us        mutex   btrfs_delayed_update_inode+0x43
           1     16.91 us     16.91 us     16.91 us      rwsem:R   btrfs_tree_read_lock_nested+0x1b
           1     15.13 us     15.13 us     15.13 us     spinlock   btrfs_getattr+0xd1
           1      6.65 us      6.65 us      6.65 us      rwsem:R   btrfs_tree_read_lock_nested+0x1b
           1      4.34 us      4.34 us      4.34 us     spinlock   process_one_work+0x1a9
  root@x1:~#
  root@x1:~# perf trace -e bpf --max-events 10 perf lock contention --use-bpf
       0.000 ( 0.013 ms): :2948281/2948281 bpf(cmd: 36, uattr: 0x7ffd5f12d730, size: 8)          = -1 EOPNOTSUPP (Operation not supported)
       0.024 ( 0.120 ms): :2948281/2948281 bpf(cmd: PROG_LOAD, uattr: 0x7ffd5f12d460, size: 148) = 16
       0.158 ( 0.034 ms): :2948281/2948281 bpf(cmd: PROG_LOAD, uattr: 0x7ffd5f12d520, size: 148) = 16
      26.653 ( 0.154 ms): perf/2948281 bpf(cmd: PROG_LOAD, uattr: 0x7ffd5f12d3d0, size: 148)     = 16
      26.825 ( 0.014 ms): perf/2948281 bpf(uattr: 0x7ffd5f12d580, size: 80)                      = 16
      87.924 ( 0.038 ms): perf/2948281 bpf(cmd: BTF_LOAD, uattr: 0x7ffd5f12d400, size: 40)       = 16
      87.988 ( 0.006 ms): perf/2948281 bpf(cmd: BTF_LOAD, uattr: 0x7ffd5f12d470, size: 40)       = 16
      88.019 ( 0.006 ms): perf/2948281 bpf(cmd: BTF_LOAD, uattr: 0x7ffd5f12d250, size: 40)       = 16
      88.029 ( 0.172 ms): perf/2948281 bpf(cmd: PROG_LOAD, uattr: 0x7ffd5f12d320, size: 148)     = 17
      88.217 ( 0.005 ms): perf/2948281 bpf(cmd: BTF_LOAD, uattr: 0x7ffd5f12d4d0, size: 40)       = 16
  root@x1:~#
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20240902200515.2103769-5-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/bpf_lock_contention.c

@@ -46,14 +46,22 @@ int lock_contention_prepare(struct lock_contention *con)
 	else
 		bpf_map__set_max_entries(skel->maps.stacks, 1);
 
-	if (target__has_cpu(target))
+	if (target__has_cpu(target)) {
+		skel->rodata->has_cpu = 1;
 		ncpus = perf_cpu_map__nr(evlist->core.user_requested_cpus);
-	if (target__has_task(target))
+	}
+	if (target__has_task(target)) {
+		skel->rodata->has_task = 1;
 		ntasks = perf_thread_map__nr(evlist->core.threads);
-	if (con->filters->nr_types)
+	}
+	if (con->filters->nr_types) {
+		skel->rodata->has_type = 1;
 		ntypes = con->filters->nr_types;
-	if (con->filters->nr_cgrps)
+	}
+	if (con->filters->nr_cgrps) {
+		skel->rodata->has_cgroup = 1;
 		ncgrps = con->filters->nr_cgrps;
+	}
 
 	/* resolve lock name filters to addr */
 	if (con->filters->nr_syms) {
@@ -82,6 +90,7 @@ int lock_contention_prepare(struct lock_contention *con)
 			con->filters->addrs = addrs;
 		}
 		naddrs = con->filters->nr_addrs;
+		skel->rodata->has_addr = 1;
 	}
 
 	bpf_map__set_max_entries(skel->maps.cpu_filter, ncpus);
@@ -90,6 +99,16 @@ int lock_contention_prepare(struct lock_contention *con)
 	bpf_map__set_max_entries(skel->maps.addr_filter, naddrs);
 	bpf_map__set_max_entries(skel->maps.cgroup_filter, ncgrps);
 
+	skel->rodata->stack_skip = con->stack_skip;
+	skel->rodata->aggr_mode = con->aggr_mode;
+	skel->rodata->needs_callstack = con->save_callstack;
+	skel->rodata->lock_owner = con->owner;
+
+	if (con->aggr_mode == LOCK_AGGR_CGROUP || con->filters->nr_cgrps) {
+		if (cgroup_is_v2("perf_event"))
+			skel->rodata->use_cgroup_v2 = 1;
+	}
+
 	if (lock_contention_bpf__load(skel) < 0) {
 		pr_err("Failed to load lock-contention BPF skeleton\n");
 		return -1;
@@ -99,7 +118,6 @@ int lock_contention_prepare(struct lock_contention *con)
 		u32 cpu;
 		u8 val = 1;
 
-		skel->bss->has_cpu = 1;
 		fd = bpf_map__fd(skel->maps.cpu_filter);
 
 		for (i = 0; i < ncpus; i++) {
@@ -112,7 +130,6 @@ int lock_contention_prepare(struct lock_contention *con)
 		u32 pid;
 		u8 val = 1;
 
-		skel->bss->has_task = 1;
 		fd = bpf_map__fd(skel->maps.task_filter);
 
 		for (i = 0; i < ntasks; i++) {
@@ -125,7 +142,6 @@ int lock_contention_prepare(struct lock_contention *con)
 		u32 pid = evlist->workload.pid;
 		u8 val = 1;
 
-		skel->bss->has_task = 1;
 		fd = bpf_map__fd(skel->maps.task_filter);
 		bpf_map_update_elem(fd, &pid, &val, BPF_ANY);
 	}
@@ -133,7 +149,6 @@ int lock_contention_prepare(struct lock_contention *con)
 	if (con->filters->nr_types) {
 		u8 val = 1;
 
-		skel->bss->has_type = 1;
 		fd = bpf_map__fd(skel->maps.type_filter);
 
 		for (i = 0; i < con->filters->nr_types; i++)
@@ -143,7 +158,6 @@ int lock_contention_prepare(struct lock_contention *con)
 	if (con->filters->nr_addrs) {
 		u8 val = 1;
 
-		skel->bss->has_addr = 1;
 		fd = bpf_map__fd(skel->maps.addr_filter);
 
 		for (i = 0; i < con->filters->nr_addrs; i++)
@@ -153,25 +167,14 @@ int lock_contention_prepare(struct lock_contention *con)
 	if (con->filters->nr_cgrps) {
 		u8 val = 1;
 
-		skel->bss->has_cgroup = 1;
 		fd = bpf_map__fd(skel->maps.cgroup_filter);
 
 		for (i = 0; i < con->filters->nr_cgrps; i++)
 			bpf_map_update_elem(fd, &con->filters->cgrps[i], &val, BPF_ANY);
 	}
 
-	/* these don't work well if in the rodata section */
-	skel->bss->stack_skip = con->stack_skip;
-	skel->bss->aggr_mode = con->aggr_mode;
-	skel->bss->needs_callstack = con->save_callstack;
-	skel->bss->lock_owner = con->owner;
-
-	if (con->aggr_mode == LOCK_AGGR_CGROUP) {
-		if (cgroup_is_v2("perf_event"))
-			skel->bss->use_cgroup_v2 = 1;
-
+	if (con->aggr_mode == LOCK_AGGR_CGROUP)
 		read_all_cgroups(&con->cgroups);
-	}
 
 	bpf_program__set_autoload(skel->progs.collect_lock_syms, false);
 

tools/perf/util/bpf_skel/lock_contention.bpf.c

@@ -117,21 +117,22 @@ struct mm_struct___new {
 } __attribute__((preserve_access_index));
 
 /* control flags */
-int enabled;
-int has_cpu;
-int has_task;
-int has_type;
-int has_addr;
-int has_cgroup;
-int needs_callstack;
-int stack_skip;
-int lock_owner;
-
-int use_cgroup_v2;
-int perf_subsys_id = -1;
+const volatile int has_cpu;
+const volatile int has_task;
+const volatile int has_type;
+const volatile int has_addr;
+const volatile int has_cgroup;
+const volatile int needs_callstack;
+const volatile int stack_skip;
+const volatile int lock_owner;
+const volatile int use_cgroup_v2;
 
 /* determine the key of lock stat */
-int aggr_mode;
+const volatile int aggr_mode;
+
+int enabled;
+
+int perf_subsys_id = -1;
 
 __u64 end_ts;