Re: CPU load due to IP networking

From: Vernon Schryver (vjs_at_calcite.rhyolite.com)
Date: 06/22/05 

Date: Wed, 22 Jun 2005 11:32:51 -0600 (MDT)

In article <1119460362.514963.187380@g47g2000cwa.googlegroups.com>,
jbl <levinjb@gmail.com> wrote:

>> >I'm looking for some data on the approximate resource cost,
>> >particularly CPU usage cost, of doing networking in a typical system,
>> >in particular a Unix-like system (linux is a suitable example) and
>> >vxworks (hence the crossposting).
>>
>> This is an extremely ill defined question. It will depend on exactly how
>> the driver is written, how the driver is accessed by the software, etc.
>
>This is why I'm interested only in rough estimates -- I should perhaps
>have added examples.

Examples would not help. The costs to do any given network task vary
by orders of magnitude depending on many things too numerous to list
here. For example, the sum of the network work and the other application
might be more or less than the sum of their parts thanks to memory
bandwidth including cache effects. You might as well ask "many miles
will a gallon of fuel move a vehicle?" An example that any third
party might find instructive such as "bicycles," "trains," "earth to
orbit rockets," would not narrow the field enough to yield answer
useful to technical people. Non-technical discussions or what I call
policitics are likley to be otherwise, but apparently random guesses
shaded according to the agenda are more honest, cheaper, and usually
more effective there.

>> The numbers you are liable to get will be so rough that you could guess
>> them just as profitably.
>>
>> Maybe if y ou told us the problem you are trying to solve, you would get
>> better answers.
>
>I'm trying to provide some guideliens for system engineers in an
>environment where a CPU is already loaded a certain amount doing
>control and telemetry with no internetworking within some allocation
>(such as, say, 75%) of available CPU bandwidth. In this case it is

Somewhat better than guessing would be to
   - take hardware and network software similar to what you might use,
   - produce a relevant synthetic application that uses 100% of the CPU,
   - run the network code and the synthetic appliation simultaneously
        and see how much each slows down.

Vernon Schryver vjs@rhyolite.com

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