io-threads: Clarify thread count range

This patch cleans up io-threads behaviour regarding the
range values that can be specified for min-threads
and max-threads. THe major change is that the min threads
have been reduced to 2 to signify that io-threads needs minimum
two threads for its operation, while keeping the default number of
threads at 16. The idea is to decouple the default thread count
from the minimum thread count.

Note to Avati:
This applies over Raghu's indentation and logging take-3 patch.

Signed-off-by: Anand V. Avati <avati@amp.gluster.com>

1 files changed, 21 insertions, 15 deletions

diff --git a/xlators/performance/io-threads/src/io-threads.c b/xlators/performance/io-threads/src/io-threads.c
index ebcb9e68c..98e212ba2 100644
--- a/xlators/performance/io-threads/src/io-threads.c
+++ b/xlators/performance/io-threads/src/io-threads.c
@@ -2168,7 +2168,7 @@ init (xlator_t *this)
 {
         iot_conf_t      *conf = NULL;
         dict_t          *options = this->options;
-        int             thread_count = IOT_MIN_THREADS;
+        int             thread_count = IOT_DEFAULT_THREADS;
         gf_boolean_t    autoscaling = IOT_SCALING_OFF;
         char            *scalestr = NULL;
         int             min_threads, max_threads;
@@ -2205,10 +2205,10 @@ init (xlator_t *this)
                                         "'autoscaling' on. Ignoring"
                                         "'thread-count' option.");
                 if (thread_count < 2)
-                        thread_count = 2;
+                        thread_count = IOT_MIN_THREADS;
         }
 
-        min_threads = IOT_MIN_THREADS;
+        min_threads = IOT_DEFAULT_THREADS;
         max_threads = IOT_MAX_THREADS;
         if (dict_get (options, "min-threads"))
                 min_threads = data_to_int32 (dict_get (options,
@@ -2247,12 +2247,12 @@ init (xlator_t *this)
         * some strange reason, make sure we set this count to
         * 2. Explained later.
         */
-        if (min_threads < 2)
-                min_threads = 2;
+        if (min_threads < IOT_MIN_THREADS)
+                min_threads = IOT_MIN_THREADS;
 
         /* Again, have atleast two. Read on. */
-        if (max_threads < 2)
-                max_threads = 2;
+        if (max_threads < IOT_MIN_THREADS)
+                max_threads = IOT_MIN_THREADS;
 
         /* This is why we need atleast two threads.
          * We're dividing the specified thread pool into
@@ -2360,15 +2360,21 @@ struct volume_options options[] = {
         { .key  = {"autoscaling"},
           .type = GF_OPTION_TYPE_BOOL
         },
-        { .key  = {"min-threads"},
-          .type = GF_OPTION_TYPE_INT,
-          .min  = IOT_MIN_THREADS,
-          .max  = IOT_MAX_THREADS
+        { .key          = {"min-threads"},
+          .type         = GF_OPTION_TYPE_INT,
+          .min          = IOT_MIN_THREADS,
+          .max          = IOT_MAX_THREADS,
+          .description  = "Minimum number of threads must be greater than or "
+                          "equal to 2. If the specified value is less than 2 "
+                          "it is adjusted upwards to 2. This is a requirement"
+                          " for the current model of threading in io-threads."
         },
-        { .key  = {"max-threads"},
-          .type = GF_OPTION_TYPE_INT,
-          .min  = IOT_MIN_THREADS,
-          .max  = IOT_MAX_THREADS
+        { .key          = {"max-threads"},
+          .type         = GF_OPTION_TYPE_INT,
+          .min          = IOT_MIN_THREADS,
+          .max          = IOT_MAX_THREADS,
+          .description  = "Maximum number of threads is advisory only so the "
+                          "user specified value will be used."
         },
 	{ .key  = {NULL} },
 };