Re: queue_work from interrupt Real time preemption2.6.11-rc2-RT-V0.7.37-03

From: Ingo Molnar
Date: Thu Feb 17 2005 - 02:54:02 EST

* David S. Miller <davem@xxxxxxxxxxxxx> wrote:

> > Maybe the networking
> > stack would break if we allowed the TIMER softirq (thread) to preempt
> > the NET softirq (threads) (and vice versa)?
> The major assumption is that softirq's run indivisibly per-cpu.
> Otherwise the per-cpu queues of RX and TX packet work would get
> corrupted.

as long as it stays on a single CPU, could we allow softirq contexts to
preempt each other? I.e. we'd keep the per-CPU assumption (that is fair
and needed for performance anyway), but we'd allow NET_TX to preempt
NET_RX and vice versa. Would this corrupt the rx/tx queues? (i suspect
it would.)

(anyway, by adding an explicit no-preempt section around the 'take
current rx queue private, then process it' on PREEMPT_RT it could be
made safe. I'm wondering whether there are any other deeper assumptions
about atomic separation of softirq contexts.)

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