Re: Basic questions on the kernel

[Stephen Samuel <samuel@bcgreen.com>]

Girish Kale wrote:
> Hi,
> 
> I have a few basic questions on the kernel performance:
> 
> 1) For embedded systems, even though standard linux may not have hard
> real-time performance unless real-time patch, low latency patch are
> applied, I would like to know if linux can give "deterministic"
> performance. Meaning can we be guaranteed that a particular process will
> be scheduled after a particular time. What are the these times or where
> do I find this data.  
You can only get "deterministic" performance if you're using a real-time
patch. I'm not sure what the timing is, but I believe that it's in the
sub-milisecond range.

You might be able to get near-realtime (but no absolute guarantees)
by setting the process that needs fast response to nice -20 this
gives it highest priority, so that it gets CPU pretty much whenever
it wants it (after device drivers).


> 
> 2) When we are using linux on an embedded system, will there a memory
> management unit for this, since there will not be any swapping in/out of
> pages? Can we avoid a process from keeping on allocating memory thereby
> starving other applications? 

Linux generally wants an MMU. Embeded kernels MAY be able to
survive without one (dunno).

Check the setrlimit call, or the ulimit bash built=in for info on
how to set resource usage limits.

You can also set limits on a system-wide basis by using the /proc mechanisms.
(your system probably has a formalized way of doing that automatically on boot..
for RedHat, that would be the file /etc/sysctl.conf )



-- 
Stephen Samuel +1(604)876-0426                samuel@bcgreen.com
		   http://www.bcgreen.com/~samuel/
Powerful committed communication, reaching through fear, uncertainty and
doubt to touch the jewel within each person and bring it to life.

-
To unsubscribe from this list: send the line "unsubscribe linux-newbie" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.linux-learn.org/faqs