JTop - Top for DROPS


JTop is a top for DROPS and Linux. It displays the installed threads and there CPU usage. For generating the graphical output, Dope is used.

JTop allows to display interactively selected threads in multiple windows, sorted by various orders. Also, a scope-view is available.


After starting, JTop opens a window containing a table with 6 columns. The columns are

By clicking in one of the column heads, the threads will be sorted according to the clicked row. Clicking again reverses the sort order.

To select some specific threads for displaying in an own window, select them using the buttons in the first column. Then press the Enter key. To close the created window, press the q key.

To change the update frequency, use the Left and Right keys.

Under Linux (and when something similar is possible under DROPS), you can zap the selected threads by pressing the k key. Of course, this requires the according privileges.

If there are more threads than the window can display at once, use the Up, Down, PgUp, PgDown, Home and End keys for scrolling.


A graphical scope allows to monitor some threads over time. It features a smoothed average and auto-adjusts to the values displayed.

To create a scope, select some threads in any of the thread windows and hit the s key. The accumulated execution times of all selected threads are monitored then. The pauses between updates of the scope can be adapted using the left and right keys when the scope has the focus. By hitting the space key, the scope changes between displaying the time since the last update and the relative load of the threads. The title bar indicates the current limit (changes with auto-adjust) and the update-pause.


The number of open windows is restricted to 32.

As of today, January 2004, there some drawing anomalies every now and then. I attribute this to the early state of the Dope widget implementation.

When using JTop with a couple of subwindows, I observed infrequent crashes of Dope. I was not able to find out whether this is related to invalid parameter passing from JTop to Dope, or some other issues inside Dope.

Performance Issues

I tested JTop under Linux on a a 1.6GHz Intel P4 with 512MB Ram. Dope had the transparency feature disabled (as of today, config_transparency in dope/server/common/main.c). With one window (about 100 threads), JTop and Dope together consume about 1% of the CPU cycles. With 11 additional windows with 10 threads each, 4% of the CPU cycles are consumed and about 12% with 32 windows. L4 test follows.

With the transparency feature enabled, there is a severe performance impact: I tested JTop under Linux and with L4/VMWare on an Athlon XP 2200+ with 512MB. With one window (about 50 threads with L4, about 100 threads with Linux), the performance seems to be ok, some percent are needed for JTop. With additional 5 windows with 5 threads each, the reactivity drops notably. With the maximum number of 32 windows, JTop/Dope was heavily overloaded.

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