sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 580 insertions, 0 deletions

diff --git a/tools/perf/perf.c b/tools/perf/perf.c
new file mode 100644
index 000000000..1f51e8de6
--- /dev/null
+++ b/tools/perf/perf.c
@@ -0,0 +1,580 @@
+/*
+ * perf.c
+ *
+ * Performance analysis utility.
+ *
+ * This is the main hub from which the sub-commands (perf stat,
+ * perf top, perf record, perf report, etc.) are started.
+ */
+#include "builtin.h"
+#include "perf.h"
+
+#include "util/build-id.h"
+#include "util/cache.h"
+#include "util/env.h"
+#include <internal/lib.h> // page_size
+#include <subcmd/exec-cmd.h>
+#include "util/config.h"
+#include <subcmd/run-command.h>
+#include "util/parse-events.h"
+#include <subcmd/parse-options.h>
+#include <subcmd/help.h>
+#include "util/debug.h"
+#include "util/event.h"
+#include "util/util.h" // usage()
+#include "ui/ui.h"
+#include "perf-sys.h"
+#include <api/fs/fs.h>
+#include <api/fs/tracing_path.h>
+#include <perf/core.h>
+#include <errno.h>
+#include <pthread.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <time.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/zalloc.h>
+
+static int use_pager = -1;
+static FILE *debug_fp = NULL;
+
+struct cmd_struct {
+	const char *cmd;
+	int (*fn)(int, const char **);
+	int option;
+};
+
+static const struct cmd_struct commands[] = {
+	{ "archive",	NULL,	0 },
+	{ "buildid-cache", cmd_buildid_cache, 0 },
+	{ "buildid-list", cmd_buildid_list, 0 },
+	{ "check",	cmd_check,	0 },
+	{ "config",	cmd_config,	0 },
+	{ "c2c",	cmd_c2c,	0 },
+	{ "diff",	cmd_diff,	0 },
+	{ "evlist",	cmd_evlist,	0 },
+	{ "help",	cmd_help,	0 },
+	{ "iostat",	NULL,	0 },
+	{ "kallsyms",	cmd_kallsyms,	0 },
+	{ "list",	cmd_list,	0 },
+	{ "record",	cmd_record,	0 },
+	{ "report",	cmd_report,	0 },
+	{ "bench",	cmd_bench,	0 },
+	{ "stat",	cmd_stat,	0 },
+#ifdef HAVE_LIBTRACEEVENT
+	{ "timechart",	cmd_timechart,	0 },
+#endif
+	{ "top",	cmd_top,	0 },
+	{ "annotate",	cmd_annotate,	0 },
+	{ "version",	cmd_version,	0 },
+	{ "script",	cmd_script,	0 },
+#ifdef HAVE_LIBTRACEEVENT
+	{ "sched",	cmd_sched,	0 },
+#endif
+#ifdef HAVE_LIBELF_SUPPORT
+	{ "probe",	cmd_probe,	0 },
+#endif
+#ifdef HAVE_LIBTRACEEVENT
+	{ "kmem",	cmd_kmem,	0 },
+	{ "lock",	cmd_lock,	0 },
+#endif
+	{ "kvm",	cmd_kvm,	0 },
+	{ "test",	cmd_test,	0 },
+#if defined(HAVE_LIBTRACEEVENT)
+	{ "trace",	cmd_trace,	0 },
+#endif
+	{ "inject",	cmd_inject,	0 },
+	{ "mem",	cmd_mem,	0 },
+	{ "data",	cmd_data,	0 },
+	{ "ftrace",	cmd_ftrace,	0 },
+	{ "daemon",	cmd_daemon,	0 },
+#ifdef HAVE_LIBTRACEEVENT
+	{ "kwork",	cmd_kwork,	0 },
+#endif
+};
+
+struct pager_config {
+	const char *cmd;
+	int val;
+};
+
+static bool same_cmd_with_prefix(const char *var, struct pager_config *c,
+				  const char *header)
+{
+	return (strstarts(var, header) && !strcmp(var + strlen(header), c->cmd));
+}
+
+static int pager_command_config(const char *var, const char *value, void *data)
+{
+	struct pager_config *c = data;
+	if (same_cmd_with_prefix(var, c, "pager."))
+		c->val = perf_config_bool(var, value);
+	return 0;
+}
+
+/* returns 0 for "no pager", 1 for "use pager", and -1 for "not specified" */
+static int check_pager_config(const char *cmd)
+{
+	int err;
+	struct pager_config c;
+	c.cmd = cmd;
+	c.val = -1;
+	err = perf_config(pager_command_config, &c);
+	return err ?: c.val;
+}
+
+static int browser_command_config(const char *var, const char *value, void *data)
+{
+	struct pager_config *c = data;
+	if (same_cmd_with_prefix(var, c, "tui."))
+		c->val = perf_config_bool(var, value);
+	if (same_cmd_with_prefix(var, c, "gtk."))
+		c->val = perf_config_bool(var, value) ? 2 : 0;
+	return 0;
+}
+
+/*
+ * returns 0 for "no tui", 1 for "use tui", 2 for "use gtk",
+ * and -1 for "not specified"
+ */
+static int check_browser_config(const char *cmd)
+{
+	int err;
+	struct pager_config c;
+	c.cmd = cmd;
+	c.val = -1;
+	err = perf_config(browser_command_config, &c);
+	return err ?: c.val;
+}
+
+static void commit_pager_choice(void)
+{
+	switch (use_pager) {
+	case 0:
+		setenv(PERF_PAGER_ENVIRONMENT, "cat", 1);
+		break;
+	case 1:
+		/* setup_pager(); */
+		break;
+	default:
+		break;
+	}
+}
+
+static int set_debug_file(const char *path)
+{
+	debug_fp = fopen(path, "w");
+	if (!debug_fp) {
+		fprintf(stderr, "Open debug file '%s' failed: %m\n",
+			path);
+		return -1;
+	}
+
+	debug_set_file(debug_fp);
+	return 0;
+}
+
+static const struct option options[] = {
+	OPT_ARGUMENT("help", "help"),
+	OPT_ARGUMENT("version", "version"),
+	OPT_ARGUMENT("exec-path", "exec-path"),
+	OPT_ARGUMENT("html-path", "html-path"),
+	OPT_ARGUMENT("paginate", "paginate"),
+	OPT_ARGUMENT("no-pager", "no-pager"),
+	OPT_ARGUMENT("debugfs-dir", "debugfs-dir"),
+	OPT_ARGUMENT("buildid-dir", "buildid-dir"),
+	OPT_ARGUMENT("list-cmds", "list-cmds"),
+	OPT_ARGUMENT("list-opts", "list-opts"),
+	OPT_ARGUMENT("debug", "debug"),
+	OPT_ARGUMENT("debug-file", "debug-file"),
+	OPT_END()
+};
+
+static int handle_options(const char ***argv, int *argc, int *envchanged)
+{
+	int handled = 0;
+
+	while (*argc > 0) {
+		const char *cmd = (*argv)[0];
+		if (cmd[0] != '-')
+			break;
+
+		/*
+		 * For legacy reasons, the "version" and "help"
+		 * commands can be written with "--" prepended
+		 * to make them look like flags.
+		 */
+		if (!strcmp(cmd, "--help") || !strcmp(cmd, "--version"))
+			break;
+
+		/*
+		 * Shortcut for '-h' and '-v' options to invoke help
+		 * and version command.
+		 */
+		if (!strcmp(cmd, "-h")) {
+			(*argv)[0] = "--help";
+			break;
+		}
+
+		if (!strcmp(cmd, "-v")) {
+			(*argv)[0] = "--version";
+			break;
+		}
+
+		if (!strcmp(cmd, "-vv")) {
+			(*argv)[0] = "version";
+			verbose = 1;
+			break;
+		}
+
+		/*
+		 * Check remaining flags.
+		 */
+		if (strstarts(cmd, CMD_EXEC_PATH)) {
+			cmd += strlen(CMD_EXEC_PATH);
+			if (*cmd == '=')
+				set_argv_exec_path(cmd + 1);
+			else {
+				puts(get_argv_exec_path());
+				exit(0);
+			}
+		} else if (!strcmp(cmd, "--html-path")) {
+			puts(system_path(PERF_HTML_PATH));
+			exit(0);
+		} else if (!strcmp(cmd, "-p") || !strcmp(cmd, "--paginate")) {
+			use_pager = 1;
+		} else if (!strcmp(cmd, "--no-pager")) {
+			use_pager = 0;
+			if (envchanged)
+				*envchanged = 1;
+		} else if (!strcmp(cmd, "--debugfs-dir")) {
+			if (*argc < 2) {
+				fprintf(stderr, "No directory given for --debugfs-dir.\n");
+				usage(perf_usage_string);
+			}
+			tracing_path_set((*argv)[1]);
+			if (envchanged)
+				*envchanged = 1;
+			(*argv)++;
+			(*argc)--;
+		} else if (!strcmp(cmd, "--buildid-dir")) {
+			if (*argc < 2) {
+				fprintf(stderr, "No directory given for --buildid-dir.\n");
+				usage(perf_usage_string);
+			}
+			set_buildid_dir((*argv)[1]);
+			if (envchanged)
+				*envchanged = 1;
+			(*argv)++;
+			(*argc)--;
+		} else if (strstarts(cmd, CMD_DEBUGFS_DIR)) {
+			tracing_path_set(cmd + strlen(CMD_DEBUGFS_DIR));
+			fprintf(stderr, "dir: %s\n", tracing_path_mount());
+			if (envchanged)
+				*envchanged = 1;
+		} else if (!strcmp(cmd, "--list-cmds")) {
+			unsigned int i;
+
+			for (i = 0; i < ARRAY_SIZE(commands); i++) {
+				const struct cmd_struct *p = commands + i;
+				printf("%s ", p->cmd);
+			}
+			putchar('\n');
+			exit(0);
+		} else if (!strcmp(cmd, "--list-opts")) {
+			unsigned int i;
+
+			for (i = 0; i < ARRAY_SIZE(options)-1; i++) {
+				const struct option *p = options + i;
+				printf("--%s ", p->long_name);
+			}
+			putchar('\n');
+			exit(0);
+		} else if (!strcmp(cmd, "--debug")) {
+			if (*argc < 2) {
+				fprintf(stderr, "No variable specified for --debug.\n");
+				usage(perf_usage_string);
+			}
+			if (perf_debug_option((*argv)[1]))
+				usage(perf_usage_string);
+
+			(*argv)++;
+			(*argc)--;
+		} else if (!strcmp(cmd, "--debug-file")) {
+			if (*argc < 2) {
+				fprintf(stderr, "No path given for --debug-file.\n");
+				usage(perf_usage_string);
+			}
+
+			if (set_debug_file((*argv)[1]))
+				usage(perf_usage_string);
+
+			(*argv)++;
+			(*argc)--;
+
+		} else {
+			fprintf(stderr, "Unknown option: %s\n", cmd);
+			usage(perf_usage_string);
+		}
+
+		(*argv)++;
+		(*argc)--;
+		handled++;
+	}
+	return handled;
+}
+
+#define RUN_SETUP	(1<<0)
+#define USE_PAGER	(1<<1)
+
+static int run_builtin(const struct cmd_struct *p, int argc, const char **argv)
+{
+	int status;
+	struct stat st;
+
+	if (use_browser == -1)
+		use_browser = check_browser_config(p->cmd);
+
+	if (use_pager == -1 && p->option & RUN_SETUP)
+		use_pager = check_pager_config(p->cmd);
+	if (use_pager == -1 && p->option & USE_PAGER)
+		use_pager = 1;
+	commit_pager_choice();
+
+	status = p->fn(argc, argv);
+	perf_config__exit();
+	exit_browser(status);
+
+	if (status)
+		return status & 0xff;
+
+	/* Somebody closed stdout? */
+	if (fstat(fileno(stdout), &st))
+		return 0;
+	/* Ignore write errors for pipes and sockets.. */
+	if (S_ISFIFO(st.st_mode) || S_ISSOCK(st.st_mode))
+		return 0;
+
+	status = 1;
+	/* Check for ENOSPC and EIO errors.. */
+	if (fflush(stdout)) {
+		fprintf(stderr, "write failure on standard output: %m\n");
+		goto out;
+	}
+	if (ferror(stdout)) {
+		fprintf(stderr, "unknown write failure on standard output\n");
+		goto out;
+	}
+	if (fclose(stdout)) {
+		fprintf(stderr, "close failed on standard output: %m\n");
+		goto out;
+	}
+	status = 0;
+out:
+	return status;
+}
+
+static void handle_internal_command(int argc, const char **argv)
+{
+	const char *cmd = argv[0];
+	unsigned int i;
+
+	/* Turn "perf cmd --help" into "perf help cmd" */
+	if (argc > 1 && !strcmp(argv[1], "--help")) {
+		argv[1] = argv[0];
+		argv[0] = cmd = "help";
+	}
+
+	for (i = 0; i < ARRAY_SIZE(commands); i++) {
+		const struct cmd_struct *p = commands+i;
+		if (p->fn == NULL)
+			continue;
+		if (strcmp(p->cmd, cmd))
+			continue;
+		exit(run_builtin(p, argc, argv));
+	}
+}
+
+static void execv_dashed_external(const char **argv)
+{
+	char *cmd;
+	const char *tmp;
+	int status;
+
+	if (asprintf(&cmd, "perf-%s", argv[0]) < 0)
+		goto do_die;
+
+	/*
+	 * argv[0] must be the perf command, but the argv array
+	 * belongs to the caller, and may be reused in
+	 * subsequent loop iterations. Save argv[0] and
+	 * restore it on error.
+	 */
+	tmp = argv[0];
+	argv[0] = cmd;
+
+	/*
+	 * if we fail because the command is not found, it is
+	 * OK to return. Otherwise, we just pass along the status code.
+	 */
+	status = run_command_v_opt(argv, 0);
+	if (status != -ERR_RUN_COMMAND_EXEC) {
+		if (IS_RUN_COMMAND_ERR(status)) {
+do_die:
+			pr_err("FATAL: unable to run '%s'", argv[0]);
+			status = -128;
+		}
+		exit(-status);
+	}
+	errno = ENOENT; /* as if we called execvp */
+
+	argv[0] = tmp;
+	zfree(&cmd);
+}
+
+static int run_argv(int *argcp, const char ***argv)
+{
+	/* See if it's an internal command */
+	handle_internal_command(*argcp, *argv);
+
+	/* .. then try the external ones */
+	execv_dashed_external(*argv);
+	return 0;
+}
+
+static int libperf_print(enum libperf_print_level level,
+			 const char *fmt, va_list ap)
+{
+	return veprintf(level, verbose, fmt, ap);
+}
+
+int main(int argc, const char **argv)
+{
+	int err, done_help = 0;
+	const char *cmd;
+
+	perf_debug_setup();
+
+	/* libsubcmd init */
+	exec_cmd_init("perf", PREFIX, PERF_EXEC_PATH, EXEC_PATH_ENVIRONMENT);
+	pager_init(PERF_PAGER_ENVIRONMENT);
+
+	libperf_init(libperf_print);
+
+	cmd = extract_argv0_path(argv[0]);
+	if (!cmd)
+		cmd = "perf-help";
+
+	srandom(time(NULL));
+
+	/* Setting $PERF_CONFIG makes perf read _only_ the given config file. */
+	config_exclusive_filename = getenv("PERF_CONFIG");
+
+	err = perf_config(perf_default_config, NULL);
+	if (err)
+		return err;
+	set_buildid_dir(NULL);
+
+	/*
+	 * "perf-xxxx" is the same as "perf xxxx", but we obviously:
+	 *
+	 *  - cannot take flags in between the "perf" and the "xxxx".
+	 *  - cannot execute it externally (since it would just do
+	 *    the same thing over again)
+	 *
+	 * So we just directly call the internal command handler. If that one
+	 * fails to handle this, then maybe we just run a renamed perf binary
+	 * that contains a dash in its name. To handle this scenario, we just
+	 * fall through and ignore the "xxxx" part of the command string.
+	 */
+	if (strstarts(cmd, "perf-")) {
+		cmd += 5;
+		argv[0] = cmd;
+		handle_internal_command(argc, argv);
+		/*
+		 * If the command is handled, the above function does not
+		 * return undo changes and fall through in such a case.
+		 */
+		cmd -= 5;
+		argv[0] = cmd;
+	}
+	if (strstarts(cmd, "trace")) {
+#ifndef HAVE_LIBTRACEEVENT
+		fprintf(stderr,
+			"trace command not available: missing libtraceevent devel package at build time.\n");
+		goto out;
+#else
+		setup_path();
+		argv[0] = "trace";
+		return cmd_trace(argc, argv);
+#endif
+	}
+	/* Look for flags.. */
+	argv++;
+	argc--;
+	handle_options(&argv, &argc, NULL);
+	commit_pager_choice();
+
+	if (argc > 0) {
+		if (strstarts(argv[0], "--"))
+			argv[0] += 2;
+	} else {
+		/* The user didn't specify a command; give them help */
+		printf("\n usage: %s\n\n", perf_usage_string);
+		list_common_cmds_help();
+		printf("\n %s\n\n", perf_more_info_string);
+		goto out;
+	}
+	cmd = argv[0];
+
+	/*
+	 * We use PATH to find perf commands, but we prepend some higher
+	 * precedence paths: the "--exec-path" option, the PERF_EXEC_PATH
+	 * environment, and the $(perfexecdir) from the Makefile at build
+	 * time.
+	 */
+	setup_path();
+	/*
+	 * Block SIGWINCH notifications so that the thread that wants it can
+	 * unblock and get syscalls like select interrupted instead of waiting
+	 * forever while the signal goes to some other non interested thread.
+	 */
+	pthread__block_sigwinch();
+
+	while (1) {
+		run_argv(&argc, &argv);
+
+		if (errno != ENOENT)
+			break;
+
+		if (!done_help) {
+			struct cmdnames main_cmds = {};
+
+			for (unsigned int i = 0; i < ARRAY_SIZE(commands); i++) {
+				add_cmdname(&main_cmds,
+					    commands[i].cmd,
+					    strlen(commands[i].cmd));
+			}
+			cmd = argv[0] = help_unknown_cmd(cmd, &main_cmds);
+			clean_cmdnames(&main_cmds);
+			done_help = 1;
+			if (!cmd)
+				break;
+		} else
+			break;
+	}
+
+	if (cmd) {
+		fprintf(stderr, "Failed to run command '%s': %m\n",
+			cmd);
+	}
+out:
+	if (debug_fp)
+		fclose(debug_fp);
+
+	return 1;
+}