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SubjectRe: interrupt cpu time accounting?
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


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