A question about the softirq implementation in DDE Linux26

Björn Döbel doebel at os.inf.tu-dresden.de
Mon Mar 1 09:25:31 CET 2010


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> I am thinking of using a lock to simulate cli/sti. When local_irq_enable() or
> local_irq_save() is called, we hold the lock; when local_irq_restore() or
> local_irq_disable(), we release the lock. We can even provide nested locking
> support if local_irq_enable() or local_irq_save() is allowed to be called
> multiple times in the same thread.

A lock does not work - been there, done that. The problem is that you
can call local_irq_disable() several times and then only call
local_irq_enable() only once to reset everything, so the semantics are
different from recursive locks.

L4Linux uses a threaded lock implementation for that reason, so we'll
discuss reusing this idea.

Bjoern
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