Re: interrupt cpu time accounting?

[Jeff Garzik <jgarzik@pobox.com>]

Robert Love wrote:
> On Sun, 2004-08-29 at 16:42 -0400, Jeff Garzik wrote:
> 
>>Does the kernel scheduler notice when a CPU spends a lot of time doing 
>>interrupt processing?
>>
>>For many network configurations you get the best cache affinity, etc. if 
>>you lock network interrupts to a single CPU.  However, on a box with 
>>high network load, that could mean that that CPU is spending more time 
>>processing interrupts than doing Real Work(tm).
>>
>>Will the scheduler "notice" this, and increasingly schedule processes 
>>away from the interrupt-heavy CPU?
> 
> 
> Nope, not explicitly anyhow.
> 
> Implicitly, at least, the load balancer will ensure that the runnable
> processes on the processor do not get "backed up" due to the delayed
> processing but you will still have the balanced minimum number of
> processes there.

What piece of code defines "balanced"?  :)


> I don't know whether the answer is to use cpu affinity and not schedule
> processes on that processor when you bind interrupts to it, or an
> automatic algorithm in the load balance for doing it, but that is a neat
> idea.

Less a neat idea, and more IMHO recognition of a problem that needs solving.

I am worried that processes will get starved if one CPU is _heavily_ 
loaded servicing interrupts, and the others are not.

Regards,

	Jeff