dyer@harvard.UUCP (Steve Dyer) (04/28/86)
Does anyone have any hard figures on the CPU overhead of running "X" on a VAXstation II which is also planned to be used as a general-purpose time-sharing machine? Anecdotally, I've been playing with one, and with one or two additional jobs running on other terminals, I can see the time-slicing during window-scrolling. It's a new experience getting swapped out in the middle of drawing a character or redrawing half a line! -- /Steve Dyer dyer@harvard.harvard.edu harvard!dyer
jg@mit-eddie.MIT.EDU (Jim Gettys) (05/01/86)
In article <902@harvard.UUCP> dyer@harvard.UUCP (Steve Dyer) writes: >Does anyone have any hard figures on the CPU overhead of running "X" >on a VAXstation II which is also planned to be used as a general-purpose >time-sharing machine? Anecdotally, I've been playing with one, and with >one or two additional jobs running on other terminals, I can see the >time-slicing during window-scrolling. It's a new experience getting >swapped out in the middle of drawing a character or redrawing half a line! The VS-2 and VS-2/RC (VAXstation II) uses the QVSS display, which is memory on the Q-Bus. There is NO hardware assist. When scrolling or painting text, therefore, the CPU is compute bound manipulating display memory. X is a user level process, and so will be timeshared like any other process. This means that in a timeshared environment, the window system will slow down in direct proportion to the timesharing (causing the pauses in the middle of character painting when some other process is running). If you are actually swapping, you need more memory in your machine. If you want to give preference to the user of the display, and don't care about penalizing other users on the machine, you can simply up the priority on the window system server. The moral here is that the VS-2 is intended to be used as a single user workstation. Displays with outboard processing power (for example, the DEC VS100 on unibus Vaxes) do much better in a timeshared environment. We have run X on as many as four of them on a single VAX 11/750 here without much problem. (Of course, a time shared 11/750 is much less useful than a microVAX.) A VAXstation II/GPX might also be more viable in this situation, though we have not run any in this fashion at MIT (my GPX is ALL MINE, thank you! :-) ). Jim Gettys Digital Equipment Corporation MIT Project Athena