Date: Wed, 08 Mar 2000 16:33:48 -0700
From: "Jeff V. Merkey" <jmerkey@timpanogas.com>
FYI. Earlier versions of Windows NT had this same problem (and it still
does). The way they got around it was to "cheat" by cranking up the
priority of the console an Windows GUI subsystem anytime someone hit a
key or moved the mouse. In fact, an NT server is still heavily loaded,
but by making the display look and feel "snappy", it presents the
illusion that the server has great responsiveness under heavy load.
This stuff in NT is all hard coded (Since their GUI is tightly
integrated with the OS), and if Linux wanted to do the same, the X
Server and bash would probably be the places to do this .....
I wouldn't call this cheating at all. There are a number of classical
tradeoffs that you have to contend with when doing scheduler design.
One is the tradeoff between efficiency and responsiveness. Switching
between tasks costs, and so if you have a very heavily loaded batch
system, it's most effiencient to set the scheduling quantuum very high,
so that a process runs for long periods of time before some other
process runs. On the other hand, for a desktop system, where user
interaction is important, you want to set the scheduling quantuum as
short as possible.
Linux does something similar, in terms rewarding processes that give up
their timeslice before their scheduling quantuum is up, and giving less
priority to CPU-bound processes. NT is simply taking it to the next
level, and rewarding user-interaction more than other I/O bound
processes. Since NT doesn't have an X server, they have to bump up the
priority of the W32 subsystem when it's in the middle of doing graphics.
The equivalent analogue for us on the Unix side is to run the X server
at a slightly high priority. (Say, nice -4).
This isn't cheating; it's just making a policy statement that user
interaction is more important that some of the other things that the
machine might be doing. If a 10 minute kernel compile takes an extra 10
seconds to complete, it's not a big deal. But if mouse motion and
keyboard response takes an extra 10 milliseconds, it is a very big deal
as far as the user is concerned.
- Ted
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