diff --git a/tools/acrntrace/README.rst b/tools/acrntrace/README.rst
index 433f161b0..9a488df33 100644
--- a/tools/acrntrace/README.rst
+++ b/tools/acrntrace/README.rst
@@ -21,8 +21,6 @@ Options:
 -i period               specify polling interval in milliseconds [1-999]
 -t max_time             max time to capture trace data (in second)
 -c                      clear the buffered old data
--r free_space           amount of free space (in MB) remaining on the disk
-                        before acrntrace stops
 
 The ``acrntrace_format.py`` is a offline tool for parsing trace data (as output
 by acrntrace) to human-readable formats based on given format.
@@ -92,12 +90,8 @@ data to your linux system, and running the analysis tool.
 
       # acrntrace
 
-   512MB storage space will be reserved by default. This ensures that acrntrace
-   will exit automatically when the free storage space on the disk is less than
-   reserved space. Reserved space on the disk is configurable through '-r'.
-
-   Trace files are created under ``./acrntrace/``, with a
-   date-time-based directory name such as ``20171115-101605``
+   Trace files are created under current directory where we launch acrntrace,
+   with a date-time-based directory name such as ``./acrntrace/20171115-101605``
 
 #. When done, stop a running ``acrntrace``, with:
 
diff --git a/tools/acrntrace/acrntrace.c b/tools/acrntrace/acrntrace.c
index 39fda35cf..436b6954d 100644
--- a/tools/acrntrace/acrntrace.c
+++ b/tools/acrntrace/acrntrace.c
@@ -29,7 +29,7 @@ static int exiting = 0;
 
 /* for opt */
 static uint64_t period = 10000;
-static const char optString[] = "i:hcr:t:";
+static const char optString[] = "i:hct:";
 static const char dev_prefix[] = "acrn_trace_";
 
 static uint32_t flags;
@@ -41,7 +41,7 @@ static int pcpu_num = 0;
 static void display_usage(void)
 {
 	printf("acrntrace - tool to collect ACRN trace data\n"
-	       "[Usage] acrntrace [-i] [period in msec] [-ch]\n\n"
+	       "[Usage] acrntrace [-i period] [-t max_time] [-ch]\n\n"
 	       "[Options]\n"
 	       "\t-h: print this message\n"
 	       "\t-i: period_in_ms: specify polling interval [1-999]\n"