Rewrite README.md

README.md

@@ -2,37 +2,59 @@
 
 Copyright (c) 2019-2022 [Antmicro](https://www.antmicro.com)
 
-This is a simple python tool that uses "sysstat" ("sar") and "gnuplot" to plot cpu and ram usage.
+This is a simple python tool that uses "sysstat" ("sar") to save information on CPU, RAM and disk usage.
+The process runs in background and can be controlled with a set of sargraph sub-commands.
+
+The tool can use "gnuplot" to optionally plot the data it collected.
+Supported plot formats are PNG and SVG, they are determined by filenames.
+
+
+# Example graph
+
+![graph](graph.png)
+
 
 # Usage
+All sargraph commands use the following pattern:
+```
+$ ./sargraph.py [session_name] [command] [args...]
+```
+
+## Starting a session
+Start a background session and name it `example`:
 ```
-$ python sargraph.py [session_name] [command] [arg]
+$ ./sargraph.py example start
 ```
 
-Background use (requires "screen" tool):
+The data will be saved in `example.txt`.
+Logs from screen will be written to `example.log`.
 
+## Adding a label
+Add labels that will be placed as comments in the collected dataset.
+They will be also visible on the plots:
 ```
-$ python3 sargraph.py chart start
-$ sleep 1
-$ python3 sargraph.py chart label "label1"
-$ sleep 1
-$ python3 sargraph.py chart label "label2"
-$ sleep 1
-$ python3 sargraph.py chart stop
+$ ./sargraph.py example label "Compilation start"
 ```
 
-Or just:
+## Plotting a running session
+Plot data collected so far in a still running session:
 ```
-$ python3 sargraph.py
-# wait 1 sec
-# type label1\n
-# wait 1 sec
-# type label2\n
-# wait 1 sec
-# type q\n
-# wait until sargraph generates plot.png
+$ ./sargraph.py example save plot.svg
 ```
 
-# Example graph
+## Plotting a closed session
+Plot data collected in a session that is not running anymore.
+```
+$ ./sargraph.py example plot plot.png
+```
+The command requires the `example.txt` log file to be present in the working directory.
+
+## Stopping a session
+Stop a session and create a final `plot.png` plot file if no other plot was created so far:
+```
+$ ./sargraph.py example stop
+```
+
+The filename of the final plot can be changed if its placed after the `stop` command.
+If the name is `none` then no plot will be created.
 
-![graph](graph.png)