Re: softirq in pre3 and all linux ports

[Andrea Arcangeli]

On Wed, Jun 20, 2001 at 01:33:19PM +1000, Paul Mackerras wrote:
> Well, I object to the "without thinking" bit. [..]

agreed, apologies.

> BHs disabled is buggy - why would you want to do that?  And if we do

tasklet_schedule

> want to allow that, shouldn't we put the check in raise_softirq or the
> equivalent, to get the minimum latency?

We should release the stack before running the softirq (some place uses
softirqs to release the stack and avoid overflows).

> Soft irqs should definitely not be much heavier than an irq handler,
> if they are then we have implemented them wrongly somehow.

ip + tcp are more intensive than just queueing a packet in a blacklog.
That's why they're not done in irq context in first place.

> ksoftirqd seems like the wrong solution to the problem to me, if we
> really getting starved by softirqs then we need to look at whether
> whatever is doing it should be a kernel thread itself rather than
> doing it in softirqs.  Do you have a concrete example of the
> starvation/live lockup that you can describe to us?

I don't have gigabit ethernet so I cannot flood my boxes to death.
But I think it's real, and a softirq marking itself runnable again is
another case to handle without live lockups or starvation.

Andrea