A question about the softirq implementation in DDE Linux26

Björn Döbel doebel at os.inf.tu-dresden.de
Fri Feb 26 18:35:14 CET 2010


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Dirk Vogt wrote:
> On Fri, 2010-02-26 at 22:08 +0800, Da Zheng wrote:
>> In Linux local_irq_save() disables irqs in the local processor, so if
>> the hard
>> IRQ handler tries to raise softirq, it is guaranteed that the softirq
>> thread
>> will not be scheduled to run, and vice versa. How would that work on a
>> SMP machine? 
> 
> Correct me if I am wrong, but i think even on native Linux the hard IRQ
> handler and the soft IRQ handler could run on the same time (on two
> different processors) as only *local* interrupts are disabled.

Christian just pointed out that the raised softirq is required to run on
the CPU the Hard-IRQ was raised on, although I can't find a resource on
that right now.

So, if this is the case, Da Zheng might have found a lingering bug.
Thanks, we'll check that.

Bjoern
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