More redis.conf self-documentation. Now even queries that took exactly server.slow_log_slower_than are logged, as this is not exact but is more intuitive for people, and a value of 0 will force every query to be logged.

redis.conf

@@ -327,7 +327,13 @@ auto-aof-rewrite-min-size 64mb
 # slow log. When a new command is logged the oldest one is removed from the
 # queue of logged commands.
 
+# The following time is expressed in microseconds, so 1000000 is equivalent
+# to one second. Note that a negative number disables the slow log, while
+# a value of zero forces the logging of every command.
 slowlog-log-slower-than 10000
+
+# There is no limit to this length. Just be aware that it will consume memory.
+# You can reclaim memory used by the slow log with SLOWLOG RESET.
 slowlog-log-len 1024
 
 ############################### ADVANCED CONFIG ###############################

src/slowlog.c

@@ -55,7 +55,7 @@ void slowlogInit(void) {
  * configured max length. */
 void slowlogPushEntryIfNeeded(robj **argv, int argc, long long duration) {
     if (server.slowlog_log_slower_than < 0) return; /* Slowlog disabled */
-    if (duration > server.slowlog_log_slower_than)
+    if (duration >= server.slowlog_log_slower_than)
         listAddNodeHead(server.slowlog,slowlogCreateEntry(argv,argc,duration));
 
     /* Remove old entries if needed. */