turbostat plugin: add new setting `RestoreAffinityPolicy`

This new setting controls how the affinity is restored during
turbostat_read(). Two policies are implemented: AffinityRestore, and
AffinityAllCPUs. The default policy, AffinityRestore, behaves exactly
the same as before, which is to save affinity and to later restore it.
The second policy, RestoreAllCPUs, skips saving the affinity and
sets the affinity to all CPUs after each read. This second policy is
useful for systems where sched_getaffinity() fails and prevents data
collection.

diff --git a/src/turbostat.c b/src/turbostat.c
index f5d3b35..ca87219 100644 (file)
--- a/src/turbostat.c
+++ b/src/turbostat.c
@@ -49,6 +49,15 @@
 
 #define PLUGIN_NAME "turbostat"
 
+typedef enum affinity_policy_enum {
+  policy_restore_affinity, /* restore cpu affinity to whatever it was before */
+  policy_allcpus_affinity, /* do not restore affinity, set to all cpus */
+  policy_invalid
+} affinity_policy_t;
+
+/* the default is to preserve cpu affinity */
+static affinity_policy_t affinity_policy = policy_restore_affinity;
+
 /*
  * This tool uses the Model-Specific Registers (MSRs) present on Intel
  * processors.
@@ -244,6 +253,7 @@ static const char *config_keys[] = {
     "TCCActivationTemp",
     "RunningAveragePowerLimit",
     "LogicalCoreNames",
+    "RestoreAffinityPolicy",
 };
 static const int config_keys_num = STATIC_ARRAY_SIZE(config_keys);
 
@@ -1454,9 +1464,32 @@ err:
   return ret;
 }
 
+int save_affinity(void) {
+  if (affinity_policy == policy_restore_affinity) {
+    /* Try to save the scheduling affinity, as it will be modified by
+    * get_counters.
+    */
+    if (sched_getaffinity(0, cpu_saved_affinity_setsize,
+                          cpu_saved_affinity_set) != 0)
+      return -1;
+  }
+
+  return 0;
+}
+
+void restore_affinity(void) {
+  /* Let's restore the affinity to the value saved in save_affinity */
+  if (affinity_policy == policy_restore_affinity)
+    (void)sched_setaffinity(0, cpu_saved_affinity_setsize,
+                            cpu_saved_affinity_set);
+  else {
+    /* reset the affinity to all present cpus */
+    (void)sched_setaffinity(0, cpu_present_setsize, cpu_present_set);
+  }
+}
+
 static int turbostat_read(void) {
   int ret;
-  int sched_getaffinity_ret;
 
   if (!allocated) {
     if ((ret = setup_all_buffers()) < 0)
@@ -1474,12 +1507,10 @@ static int turbostat_read(void) {
     }
   }
 
-  /* Try to save the scheduling affinity, as it will be modified by
-   * get_counters. If the call is unsuccessfull, this will be handled later
-   * on by restoring affinity to cpu_present_set instead.
-   */
-  sched_getaffinity_ret =
-      sched_getaffinity(0, cpu_saved_affinity_setsize, cpu_saved_affinity_set);
+  if (save_affinity() != 0) {
+    ERROR("turbostat plugin: Unable to save the CPU affinity");
+    return -1;
+  }
 
   if (!initialized) {
     if ((ret = for_all_cpus(get_counters, EVEN_COUNTERS)) < 0)
@@ -1514,21 +1545,8 @@ static int turbostat_read(void) {
   }
   ret = 0;
 out:
-  /*
-   * Let's restore the affinity
-   * This might fail if the number of CPU changed, but we can't do anything in
-   * that case..
-   */
-  if (sched_getaffinity_ret == 0)
-    (void)sched_setaffinity(0, cpu_saved_affinity_setsize,
-                            cpu_saved_affinity_set);
-  else {
-    /*
-     * The previous call to sched_getaffinity() failed, so
-     * reset the affinity to all present cpus.
-     */
-    (void)sched_setaffinity(0, cpu_present_setsize, cpu_present_set);
-  }
+  restore_affinity();
+
   return ret;
 }
 
@@ -1599,6 +1617,15 @@ err:
   return ret;
 }
 
+affinity_policy_t parse_affinity_policy(const char *value) {
+  if (strcasecmp("AffinityRestore", value) == 0)
+    return policy_restore_affinity;
+  else if (strcasecmp("AffinityAllCPUs", value) == 0)
+    return policy_allcpus_affinity;
+
+  return policy_invalid;
+}
+
 static int turbostat_config(const char *key, const char *value) {
   long unsigned int tmp_val;
   char *end;
@@ -1645,6 +1672,13 @@ static int turbostat_config(const char *key, const char *value) {
       return -1;
     }
     tcc_activation_temp = (unsigned int)tmp_val;
+  } else if (strcasecmp("RestoreAffinityPolicy", key) == 0) {
+    affinity_policy = parse_affinity_policy(value);
+    if (affinity_policy == policy_invalid) {
+      /* set to default policy if requested policy is invalid */
+      affinity_policy = policy_restore_affinity;
+      ERROR("turbostat plugin: Invalid RestoreAffinityPolicy '%s'", value);
+    }
   } else {
     ERROR("turbostat plugin: Invalid configuration option '%s'", key);
     return -1;