Low priority processes

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2 total messages Started by LOMAX Fri, 27 Jan 1989 15:57

#2445

Author: LOMAX
Date: Fri, 27 Jan 1989 15:57

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  Can anybody out there enlighten me as to how a single processor handles
multiple processes waiting for communications. Do these waiting processes use
any CPU time, and do they differ depending on whether they are waiting on hard
or soft channels.

                      Tony Lomax....

P.S.

 The reason for asking is that I wish to make absolute measurements of CPU time
for a particular process and I therefore need to know if waiting processes will
add to the measured CPU time.

Re: Low priority processes

#2446

Author: Colin Plumb
Date: Sat, 28 Jan 1989 06:13

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LOMAX@bio-medical-physics.aberdeen.ac.uk wrote:
>   Can anybody out there enlighten me as to how a single processor handles
> multiple processes waiting for communications. Do these waiting processes use
> any CPU time, and do they differ depending on whether they are waiting on hard
> or soft channels.

A process waiting for communication uses only memory, not CPU cycles.
Of course, copying the message (whether it's by a soft channel or DMA
from a link) does take memory cycles, and the latter can occur even if
the process isn't running.

Things that can take CPU resources away from a running process:
- The timer waking up a process
- A link communicating or finishing and waking up a process
- The event channel waking up a process
- Time-slicing at the low priority level
- For completeness, the reset pin has the obvious effects

Everything else is in response to some explicit action by the currently
running process.

I've had demos with 16000 processes runnning around.  If they were all
sleeping, I could have a quarter of a million.
-- 
	-Colin (uunet!microsof!w-colinp)

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