performance/write-behind: add option "enable-trickling-writes".

- With this option enabled, writes are stack-wound even though not enough
    data is aggregated, provided there are no write-requests which are
    stack-wound but reply is yet to come. The reason behind this option
    is to make use of the network, which is relatively free (with no writes
    or replies in transit). However, with non-standard block-sizes of writes
    the performance can actually degrade. Hence making this configurable.

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

BUG: 276 (write behind needs to be optimized.)
URL: http://bugs.gluster.com/cgi-bin/bugzilla3/show_bug.cgi?id=276

1 files changed, 41 insertions, 22 deletions

diff --git a/xlators/performance/write-behind/src/write-behind.c b/xlators/performance/write-behind/src/write-behind.c
index 1006b730a..10e8ec4b1 100644
--- a/xlators/performance/write-behind/src/write-behind.c
+++ b/xlators/performance/write-behind/src/write-behind.c
@@ -88,6 +88,7 @@ struct wb_conf {
         uint64_t     disable_till;
         gf_boolean_t enable_O_SYNC;
         gf_boolean_t flush_behind;
+        gf_boolean_t enable_trickling_writes;
 };
 
 
@@ -114,7 +115,7 @@ wb_sync (call_frame_t *frame, wb_file_t *file, list_head_t *winds);
 
 ssize_t
 __wb_mark_winds (list_head_t *list, list_head_t *winds, size_t aggregate_size,
-                 char wind_all);
+                 char wind_all, char enable_trickling_writes);
 
 
 static void
@@ -1379,17 +1380,22 @@ __wb_can_wind (list_head_t *list, size_t aggregate_conf,
 
 ssize_t
 __wb_mark_winds (list_head_t *list, list_head_t *winds, size_t aggregate_conf,
-                 char wind_all)
+                 char wind_all, char enable_trickling_writes)
 {
-        size_t   size = 0;
-        char     incomplete_writes = 0;
-        char     other_fop_in_queue = 0;
-        char     non_contiguous_writes = 0;
+        size_t   size                   = 0;
+        char     other_fop_in_queue     = 0;
+        char     incomplete_writes      = 1; 
+        char     non_contiguous_writes  = 0;
         char     enough_data_aggregated = 0;
+        char    *trickling_writes       = NULL;
+
+        if (enable_trickling_writes) {
+                trickling_writes = &incomplete_writes;
+        }
 
         if (!wind_all) {
                 __wb_can_wind (list, aggregate_conf, &other_fop_in_queue,
-                               &non_contiguous_writes, &incomplete_writes,
+                               &non_contiguous_writes, trickling_writes,
                                &enough_data_aggregated);
         }
 
@@ -1700,7 +1706,8 @@ wb_process_queue (call_frame_t *frame, wb_file_t *file, char flush_all)
 
                 if (count == 0) {
                         __wb_mark_winds (&file->request, &winds, size,
-                                         flush_all);
+                                         flush_all,
+                                         conf->enable_trickling_writes);
                 }
 
         }
@@ -2278,10 +2285,7 @@ init (xlator_t *this)
 {
         dict_t    *options = NULL;
         wb_conf_t *conf = NULL;
-        char      *window_size_string    = NULL;
-        char      *flush_behind_string   = NULL;
-        char      *disable_till_string = NULL;
-        char      *enable_O_SYNC_string = NULL;
+        char      *str = NULL;
         int32_t    ret = -1;
 
         if ((this->children == NULL)
@@ -2309,9 +2313,9 @@ init (xlator_t *this)
         
         conf->enable_O_SYNC = _gf_false;
         ret = dict_get_str (options, "enable-O_SYNC",
-                            &enable_O_SYNC_string);
+                            &str);
         if (ret == 0) {
-                ret = gf_string2boolean (enable_O_SYNC_string,
+                ret = gf_string2boolean (str,
                                          &conf->enable_O_SYNC);
                 if (ret == -1) {
                         gf_log (this->name, GF_LOG_ERROR,
@@ -2324,15 +2328,15 @@ init (xlator_t *this)
         conf->aggregate_size = WB_AGGREGATE_SIZE;
         conf->disable_till = 1;
         ret = dict_get_str (options, "disable-for-first-nbytes", 
-                            &disable_till_string);
+                            &str);
         if (ret == 0) {
-                ret = gf_string2bytesize (disable_till_string, 
+                ret = gf_string2bytesize (str, 
                                           &conf->disable_till);
                 if (ret != 0) {
                         gf_log (this->name, GF_LOG_ERROR, 
                                 "invalid number format \"%s\" of \"option "
                                 "disable-for-first-nbytes\"", 
-                                disable_till_string);
+                                str);
                         return -1;
                 }
         }
@@ -2344,15 +2348,15 @@ init (xlator_t *this)
         /* configure 'option window-size <size>' */
         conf->window_size = WB_WINDOW_SIZE; 
         ret = dict_get_str (options, "cache-size", 
-                            &window_size_string);
+                            &str);
         if (ret == 0) {
-                ret = gf_string2bytesize (window_size_string, 
+                ret = gf_string2bytesize (str, 
                                           &conf->window_size);
                 if (ret != 0) {
                         gf_log (this->name, GF_LOG_ERROR, 
                                 "invalid number format \"%s\" of \"option "
                                 "window-size\"", 
-                                window_size_string);
+                                str);
                         FREE (conf);
                         return -1;
                 }
@@ -2378,9 +2382,9 @@ init (xlator_t *this)
         /* configure 'option flush-behind <on/off>' */
         conf->flush_behind = 0;
         ret = dict_get_str (options, "flush-behind", 
-                            &flush_behind_string);
+                            &str);
         if (ret == 0) {
-                ret = gf_string2boolean (flush_behind_string, 
+                ret = gf_string2boolean (str, 
                                          &conf->flush_behind);
                 if (ret == -1) {
                         gf_log (this->name, GF_LOG_ERROR,
@@ -2393,6 +2397,21 @@ init (xlator_t *this)
 				"enabling flush-behind");
                 }
         }
+
+        conf->enable_trickling_writes = _gf_true;
+        ret = dict_get_str (options, "enable-trickling-writes",
+                            &str);
+        if (ret == 0) {
+                ret = gf_string2boolean (str,
+                                         &conf->enable_trickling_writes);
+                if (ret == -1) {
+                        gf_log (this->name, GF_LOG_ERROR,
+                                "'enable-trickling_writes' takes only boolean"
+                                " arguments");
+                        return -1;
+                }
+        }
+
         this->private = conf;
         return 0;
 }