Newsgroups: comp.windows.x
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!think.com!mintaka!bloom-beacon!dont-send-mail-to-path-lines
From: thp@westhawk.UUCP ("Timothy H Panton.")
Subject: Re: Robust multi-display clients
Message-ID: <9105121025.AA06635@westhawk.uucp>
Sender: westhawk!thp@uunet.uu.net
Organization: The Internet
Date: 12 May 91 10:25:08 GMT
Lines: 35


> der Mouse <mouse@lightning.mcrcim.mcgill.edu>
>>  Buehring@intellection.com
>> Disadvantage:
>>         - You may end up context switching your guts out.
> 
> I think this will probably not turn out to be a problem.
... EMACS example elided ....
> The above scenario includes 9 switches between kernel mode and user
> mode on xt3, with only one user process involved.  On lightning, there
> are 21 switches between kernel mode and user mode, with a minimum of 4
> switches from one user-level context to another.
And all that is for one keystroke! 

If the events are coming from another program like a simulation engine
producing a few hundred new values every 1/10th of a second you have to
be a little more careful. I found that in a particular case we lost about
20% of the CPU to context switching. I had to rework the frontend - backend
link so that it was polled every 1/2 second rather than using a signal
based fast turnaround method, this got us back below 10% overhead on most
machines. It seemed to cripple an early Mips machine (I'm still not
sure why, neither were MIPS UK.).

It sounds like your situatuion is nearer mine than Mouses', in which case
I advise you to be very careful when you design the IPC stuff, separate
process _is_ the way to go, but it isn't problem free.

Tim.
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