[dpdk-dev] [PATCH 3/3] power: check if userspace governor is available

[Radoslaw Biernacki <radoslaw.biernacki@linaro.org>]

Since for new Intel CPU's kernel use intel_pstate driver, which does
not offer userspace governor, it is wise to check the userspace
governor availability before trying to perform governor switch. The
outcome from this patch is direct information for user about the root
cause of failure during the rte_power_acpi_cpufreq_init().

Signed-off-by: Radoslaw Biernacki <radoslaw.biernacki@linaro.org>
---
 lib/librte_power/rte_power_acpi_cpufreq.c | 74 +++++++++++++++++++++++++++++++
 1 file changed, 74 insertions(+)

diff --git a/lib/librte_power/rte_power_acpi_cpufreq.c b/lib/librte_power/rte_power_acpi_cpufreq.c
index f811bd3..0d9a2a5 100644
--- a/lib/librte_power/rte_power_acpi_cpufreq.c
+++ b/lib/librte_power/rte_power_acpi_cpufreq.c
@@ -65,6 +65,11 @@
 #define POWER_CONVERT_TO_DECIMAL 10
 
 #define POWER_GOVERNOR_USERSPACE "userspace"
+#define POWER_SCALING_DRIVER_INTEL_PSTATE "intel_pstate"
+#define POWER_SYSFILE_SCALING_DRIVER \
+		"/sys/devices/system/cpu/cpu%u/cpufreq/scaling_driver"
+#define POWER_SYSFILE_AVAIL_GOVERNOR \
+		"/sys/devices/system/cpu/cpu%u/cpufreq/scaling_available_governors"
 #define POWER_SYSFILE_GOVERNOR   \
 		"/sys/devices/system/cpu/cpu%u/cpufreq/scaling_governor"
 #define POWER_SYSFILE_AVAIL_FREQ \
@@ -139,6 +144,70 @@ set_freq_internal(struct rte_power_info *pi, uint32_t idx)
 	return 1;
 }
 
+/* check /sys file for presence of given string */
+static int
+power_check_sysfile_string(const char *fullpath, const char *string)
+{
+	int fd;
+	int count;
+	int ret = -1;
+	char buf[BUFSIZ];
+
+	fd = open(fullpath, O_RDONLY);
+	if (fd < 0) {
+		RTE_LOG(ERR, POWER, "Failed to open %s\n", fullpath);
+		return ret;
+	}
+
+	count = read(fd, buf, sizeof(buf));
+	if (count < 0) {
+		RTE_LOG(ERR, POWER, "Failed to read from %s\n", fullpath);
+		goto out;
+	}
+	buf[min((size_t)count, sizeof(buf)-1)] = '\0';
+
+	if (strstr(buf, string))
+		ret = 0; /* substring found */
+
+out:
+	if (close(fd)) {
+		RTE_LOG(ERR, POWER, "Error while closing file %s\n", fullpath);
+		return -1;
+	}
+
+	return ret;
+}
+
+/* check if userspace governor is offered by the kernel */
+static int power_check_gov_userspace(unsigned int lcore_id)
+{
+	char fullpath[PATH_MAX];
+
+	snprintf(fullpath, sizeof(fullpath),
+		 POWER_SYSFILE_AVAIL_GOVERNOR, lcore_id);
+	if (power_check_sysfile_string(
+		fullpath, POWER_GOVERNOR_USERSPACE)) {
+
+		RTE_LOG(ERR, POWER, "Userspace governor is not available\n");
+
+		snprintf(fullpath, sizeof(fullpath),
+			 POWER_SYSFILE_SCALING_DRIVER, lcore_id);
+		if (!power_check_sysfile_string(
+			fullpath, POWER_SCALING_DRIVER_INTEL_PSTATE)) {
+
+			RTE_LOG(WARNING, POWER,
+				POWER_SCALING_DRIVER_INTEL_PSTATE "was detected"
+				" which does not offer userspace power governor"
+				". \"intel_pstate=disable\" needs to be added "
+				"to the kernel boot parameters.\n");
+		}
+
+		return -1;
+	}
+
+	return 0;
+}
+
 /**
  * It is to check the current scaling governor by reading sys file, and then
  * set it into 'userspace' if it is not by writing the sys file. The original
@@ -154,6 +223,11 @@ power_set_governor(unsigned int lcore_id, const char *new_gov, char *old_gov,
 	char buf[BUFSIZ];
 	char fullpath[PATH_MAX];
 
+	/* check if userspace governor is available */
+	if (power_check_gov_userspace(lcore_id))
+		return ret;
+
+	/* store current governor and set userspace governor */
 	snprintf(fullpath, sizeof(fullpath), POWER_SYSFILE_GOVERNOR,
 		 lcore_id);
 	fd = open(fullpath, O_RDWR);
-- 
2.7.4