tools/power/x86/intel-speed-select: Use cgroup isolate for CPU 0

From kernel version 6.5, CPU 0 hotplug capability is deprecated.
If some SST profile doesn't have CPU 0, then it is no longer possible to
offline CPU 0. This means that user space threads will still run on
CPU 0.

To workaround this issue, use cgroup v2 isolation feature. Whenever there
/sys/devices/system/cpu/cpu0/online file is absent or open fails, isolate
CPU 0 via CPU cgroup v2 isolation. Also add a command line option to
force even if the /sys/devices/system/cpu/cpu0/online is present.

The previous commit "01bcb56f059e ("tools/power/x86/intel-speed-select:
Prevent CPU 0 offline") was just warning about this issue based on the
kernel version 6.5 and above. With this new approach, instead of warning
take action to mitigate the issue.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>

Author: spandruvada

tools/power/x86/intel-speed-select/isst-config.c

@@ -6,7 +6,6 @@
 
 #include <ctype.h>
 #include <linux/isst_if.h>
-#include <sys/utsname.h>
 
 #include "isst.h"
 
@@ -56,6 +55,8 @@ static int clos_min = -1;
 static int clos_max = -1;
 static int clos_desired = -1;
 static int clos_priority_type;
+static int cpu_0_cgroupv2;
+static int cpu_0_workaround(int isolate);
 
 struct _cpu_map {
 	unsigned short core_id;
@@ -475,52 +476,26 @@ static unsigned int is_cpu_online(int cpu)
 	return online;
 }
 
-static int get_kernel_version(int *major, int *minor)
-{
-	struct utsname buf;
-	int ret;
-
-	ret = uname(&buf);
-	if (ret)
-		return ret;
-
-	ret = sscanf(buf.release, "%d.%d", major, minor);
-	if (ret != 2)
-		return ret;
-
-	return 0;
-}
-
-#define CPU0_HOTPLUG_DEPRECATE_MAJOR_VER	6
-#define CPU0_HOTPLUG_DEPRECATE_MINOR_VER	5
-
 void set_cpu_online_offline(int cpu, int state)
 {
 	char buffer[128];
 	int fd, ret;
 
-	if (!cpu) {
-		int major, minor;
-
-		ret = get_kernel_version(&major, &minor);
-		if (!ret) {
-			if (major > CPU0_HOTPLUG_DEPRECATE_MAJOR_VER || (major == CPU0_HOTPLUG_DEPRECATE_MAJOR_VER &&
-				minor >= CPU0_HOTPLUG_DEPRECATE_MINOR_VER)) {
-				debug_printf("Ignore CPU 0 offline/online for kernel version >= %d.%d\n", major, minor);
-				debug_printf("Use cgroups to isolate CPU 0\n");
-				return;
-			}
-		}
+	if (cpu_0_cgroupv2 && !cpu) {
+		fprintf(stderr, "Will use cgroup v2 for CPU 0\n");
+		cpu_0_workaround(!state);
+		return;
 	}
 
 	snprintf(buffer, sizeof(buffer),
 		 "/sys/devices/system/cpu/cpu%d/online", cpu);
 
 	fd = open(buffer, O_WRONLY);
 	if (fd < 0) {
-		if (!cpu && state) {
+		if (!cpu) {
 			fprintf(stderr, "This system is not configured for CPU 0 online/offline\n");
-			fprintf(stderr, "Ignoring online request for CPU 0 as this is already online\n");
+			fprintf(stderr, "Will use cgroup v2\n");
+			cpu_0_workaround(!state);
 			return;
 		}
 		err(-1, "%s open failed", buffer);
@@ -907,7 +882,7 @@ int enable_cpuset_controller(void)
 	return 0;
 }
 
-int isolate_cpus(struct isst_id *id, int mask_size, cpu_set_t *cpu_mask, int level)
+int isolate_cpus(struct isst_id *id, int mask_size, cpu_set_t *cpu_mask, int level, int cpu_0_only)
 {
 	int i, first, curr_index, index, ret, fd;
 	static char str[512], dir_name[64];
@@ -950,6 +925,12 @@ int isolate_cpus(struct isst_id *id, int mask_size, cpu_set_t *cpu_mask, int lev
 	curr_index = 0;
 	first = 1;
 	str[0] = '\0';
+
+	if (cpu_0_only) {
+		snprintf(str, str_len, "0");
+		goto create_partition;
+	}
+
 	for (i = 0; i < get_topo_max_cpus(); ++i) {
 		if (!is_cpu_in_power_domain(i, id))
 			continue;
@@ -972,6 +953,7 @@ int isolate_cpus(struct isst_id *id, int mask_size, cpu_set_t *cpu_mask, int lev
 		first = 0;
 	}
 
+create_partition:
 	debug_printf("isolated CPUs list: package:%d curr_index:%d [%s]\n", id->pkg, curr_index ,str);
 
 	snprintf(cpuset_cpus, sizeof(cpuset_cpus), "%s/cpuset.cpus", dir_name);
@@ -1012,6 +994,74 @@ int isolate_cpus(struct isst_id *id, int mask_size, cpu_set_t *cpu_mask, int lev
 	return 0;
 }
 
+static int cpu_0_workaround(int isolate)
+{
+	int fd, fd1, len, ret;
+	cpu_set_t cpu_mask;
+	struct isst_id id;
+	char str[2];
+
+	debug_printf("isolate CPU 0 state: %d\n", isolate);
+
+	if (isolate)
+		goto isolate;
+
+	/* First check if CPU 0 was isolated to remove isolation. */
+
+	/* If the cpuset.cpus doesn't exist, that means that none of the CPUs are isolated*/
+	fd = open("/sys/fs/cgroup/0-0-0/cpuset.cpus", O_RDONLY, 0);
+	if (fd < 0)
+		return 0;
+
+	len = read(fd, str, sizeof(str));
+	/* Error check, but unlikely to fail. If fails that means that not isolated */
+	if (len == -1)
+		return 0;
+
+
+	/* Is CPU 0 is in isolate list, the display is sorted so first element will be CPU 0*/
+	if (str[0] != '0') {
+		close(fd);
+		return 0;
+	}
+
+	fd1 = open("/sys/fs/cgroup/0-0-0/cpuset.cpus.partition", O_RDONLY, 0);
+	/* Unlikely that, this attribute is not present, but handle error */
+	if (fd1 < 0) {
+		close(fd);
+		return 0;
+	}
+
+	/* Is CPU 0 already changed partition to "member" */
+	len = read(fd1, str, sizeof(str));
+	if (len != -1 && str[0] == 'm') {
+		close(fd1);
+		close(fd);
+		return 0;
+	}
+
+	close(fd1);
+	close(fd);
+
+	debug_printf("CPU 0 was isolated before, so remove isolation\n");
+
+isolate:
+	ret = enable_cpuset_controller();
+	if (ret)
+		goto isolate_fail;
+
+	CPU_ZERO(&cpu_mask);
+	memset(&id, 0, sizeof(struct isst_id));
+	CPU_SET(0, &cpu_mask);
+
+	ret = isolate_cpus(&id, sizeof(cpu_mask), &cpu_mask, isolate, 1);
+isolate_fail:
+	if (ret)
+		fprintf(stderr, "Can't isolate CPU 0\n");
+
+	return ret;
+}
+
 static int isst_fill_platform_info(void)
 {
 	const char *pathname = "/dev/isst_interface";
@@ -1458,7 +1508,8 @@ static void set_tdp_level_for_cpu(struct isst_id *id, void *arg1, void *arg2, vo
 			if (ret)
 				goto use_offline;
 
-			ret = isolate_cpus(id, ctdp_level.core_cpumask_size, ctdp_level.core_cpumask, tdp_level);
+			ret = isolate_cpus(id, ctdp_level.core_cpumask_size,
+					   ctdp_level.core_cpumask, tdp_level, 0);
 			if (ret)
 				goto use_offline;
 
@@ -3054,6 +3105,7 @@ static void usage(void)
 	printf("\t[-n|--no-daemon : Don't run as daemon. By default --oob will turn on daemon mode\n");
 	printf("\t[-w|--delay : Delay for reading config level state change in OOB poll mode.\n");
 	printf("\t[-g|--cgroupv2 : Try to use cgroup v2 CPU isolation instead of CPU online/offline.\n");
+	printf("\t[-u|--cpu0-workaround : Don't try to online/offline CPU0 instead use cgroup v2.\n");
 	printf("\nResult format\n");
 	printf("\tResult display uses a common format for each command:\n");
 	printf("\tResults are formatted in text/JSON with\n");
@@ -3107,6 +3159,7 @@ static void cmdline(int argc, char **argv)
 		{ "no-daemon", no_argument, 0, 'n' },
 		{ "poll-interval", required_argument, 0, 'w' },
 		{ "cgroupv2", required_argument, 0, 'g' },
+		{ "cpu0-workaround", required_argument, 0, 'u' },
 		{ 0, 0, 0, 0 }
 	};
 
@@ -3137,7 +3190,7 @@ static void cmdline(int argc, char **argv)
 		goto out;
 
 	progname = argv[0];
-	while ((opt = getopt_long_only(argc, argv, "+c:df:hio:vabw:ng", long_options,
+	while ((opt = getopt_long_only(argc, argv, "+c:df:hio:vabw:ngu", long_options,
 				       &option_index)) != -1) {
 		switch (opt) {
 		case 'a':
@@ -3199,6 +3252,9 @@ static void cmdline(int argc, char **argv)
 		case 'g':
 			cgroupv2 = 1;
 			break;
+		case 'u':
+			cpu_0_cgroupv2 = 1;
+			break;
 		default:
 			usage();
 		}

tools/power/x86/intel-speed-select/isst-daemon.c

@@ -90,7 +90,8 @@ void process_level_change(struct isst_id *id)
 		if (ret)
 			goto use_offline;
 
-		isolate_cpus(id, ctdp_level.core_cpumask_size, ctdp_level.core_cpumask, pkg_dev.current_level);
+		isolate_cpus(id, ctdp_level.core_cpumask_size, ctdp_level.core_cpumask,
+			     pkg_dev.current_level, 0);
 
 		goto free_mask;
 	}

tools/power/x86/intel-speed-select/isst.h

@@ -318,7 +318,8 @@ extern struct isst_platform_ops *tpmi_get_platform_ops(void);
 
 /* Cgroup related interface */
 extern int enable_cpuset_controller(void);
-extern int isolate_cpus(struct isst_id *id, int mask_size, cpu_set_t *cpu_mask, int level);
+extern int isolate_cpus(struct isst_id *id, int mask_size, cpu_set_t *cpu_mask,
+			int level, int cpu_0_only);
 extern int use_cgroupv2(void);
 
 #endif