Commit 968ebff1 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup, perf_event: make perf_event controller work on cgroup2 hierarchy 



perf_event is a utility controller whose primary role is identifying
cgroup membership to filter perf events; however, because it also
tracks some per-css state, it can't be replaced by pure cgroup
membership test.  Mark the controller as implicitly enabled on the
default hierarchy so that perf events can always be filtered based on
cgroup v2 path as long as the controller is not mounted on a legacy
hierarchy.

"perf record" is updated accordingly so that it searches for both v1
and v2 hierarchies.  A v1 hierarchy is used if perf_event is mounted
on it; otherwise, it uses the v2 hierarchy.

v2: Doc updated to reflect more flexible rebinding behavior.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
parent b807421a

Documentation/cgroup-v2.txt

+12 −0
Original line number Diff line number Diff line
@@ -49,6 +49,8 @@ CONTENTS 
    5-3-2. Writeback

  5-4. PID

    5-4-1. PID Interface Files

  5-5. Misc

    5-5-1. perf_event

6. Namespace

  6-1. Basics

  6-2. The Root and Views
@@ -1160,6 +1162,16 @@ through fork() or clone(). These will return -EAGAIN if the creation 
of a new process would cause a cgroup policy to be violated.





5-5. Misc



5-5-1. perf_event



perf_event controller, if not mounted on a legacy hierarchy, is

automatically enabled on the v2 hierarchy so that perf events can

always be filtered by cgroup v2 path.  The controller can still be

moved to a legacy hierarchy after v2 hierarchy is populated.





6. Namespace



6-1. Basics

kernel/events/core.c

+6 −0
Original line number Diff line number Diff line
@@ -10792,5 +10792,11 @@ struct cgroup_subsys perf_event_cgrp_subsys = { 
	.css_alloc	= perf_cgroup_css_alloc,

	.css_free	= perf_cgroup_css_free,

	.attach		= perf_cgroup_attach,

	/*

	 * Implicitly enable on dfl hierarchy so that perf events can

	 * always be filtered by cgroup2 path as long as perf_event

	 * controller is not mounted on a legacy hierarchy.

	 */

	.implicit_on_dfl = true,

};

#endif /* CONFIG_CGROUP_PERF */

tools/perf/util/cgroup.c

+19 −7
Original line number Diff line number Diff line
@@ -12,8 +12,8 @@ cgroupfs_find_mountpoint(char *buf, size_t maxlen) 
{

	FILE *fp;

	char mountpoint[PATH_MAX + 1], tokens[PATH_MAX + 1], type[PATH_MAX + 1];

	char path_v1[PATH_MAX + 1], path_v2[PATH_MAX + 2], *path;

	char *token, *saved_ptr = NULL;

	int found = 0;



	fp = fopen("/proc/mounts", "r");

	if (!fp)
@@ -24,31 +24,43 @@ cgroupfs_find_mountpoint(char *buf, size_t maxlen) 
	 * and inspect every cgroupfs mount point to find one that has

	 * perf_event subsystem

	 */

	path_v1[0] = '\0';

	path_v2[0] = '\0';



	while (fscanf(fp, "%*s %"STR(PATH_MAX)"s %"STR(PATH_MAX)"s %"

				STR(PATH_MAX)"s %*d %*d\n",

				mountpoint, type, tokens) == 3) {



		if (!strcmp(type, "cgroup")) {

		if (!path_v1[0] && !strcmp(type, "cgroup")) {



			token = strtok_r(tokens, ",", &saved_ptr);



			while (token != NULL) {

				if (!strcmp(token, "perf_event")) {

					found = 1;

					strcpy(path_v1, mountpoint);

					break;

				}

				token = strtok_r(NULL, ",", &saved_ptr);

			}

		}

		if (found)



		if (!path_v2[0] && !strcmp(type, "cgroup2"))

			strcpy(path_v2, mountpoint);



		if (path_v1[0] && path_v2[0])

			break;

	}

	fclose(fp);

	if (!found)



	if (path_v1[0])

		path = path_v1;

	else if (path_v2[0])

		path = path_v2;

	else

		return -1;



	if (strlen(mountpoint) < maxlen) {

		strcpy(buf, mountpoint);

	if (strlen(path) < maxlen) {

		strcpy(buf, path);

		return 0;

	}

	return -1;

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