Re: route cache DoS testing and softirqs

From: Dipankar Sarma
Date: Wed Mar 31 2004 - 02:39:51 EST

On Tue, Mar 30, 2004 at 11:29:44PM +0200, Robert Olsson wrote:
> Andrea Arcangeli writes:
> > I see what's going on now, yes my patch cannot help. the workload is
> > simply generating too much hardirq load, and it's like if we don't use
> > softirq at all but that we process the packet inside the hardirq for
> > this matter. As far as RCU is concerned it's like if there a no softirq
> > at all but that we process everything in the hardirq.
> >
> > so what you're looking after is a new feature then:
> >
> > 1) rate limit the hardirqs
> > 2) rate limit only part of the irq load (i.e. the softirq, that's handy
> > since it's already splitted out) to scheduler-aware context (not
> > inside irq context anymore)
> > 3) stop processing packets in irqs in the first place (NAPI or similar)
> No Andrea it pure softirq workload. Interfaces runs with irq disabled
> at this load w. NAPI. Softirq's are run from spin_unlock_bh etc when
> doing route lookup and GC. And the more fine-grained locking we do the
> the more do_softirq's are run.

Not lookup, we don't take the lock in lookup. Probably route
insertions which will happen very frequently in this case.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at