FreeBSD spinlock - compatibility layer

[Orit Moskovich]

>From what I've read in "FreeBSD - device drivers" book by Joseph Kong on interrupt handling, you cannot voluntarily context switch (that is, sleep) in interrupt threads .
In any case, I think that the functionality of spin mutex should remain as is, and not modified to sleep mutex, as it can be used in places that sleep mustn't be used, or that require the properties of the spin due to performance considerations.



-----Original Message-----
From: John Baldwin [mailto:jhb at freebsd.org] 
Sent: Tuesday, May 21, 2013 10:02 PM
To: Orit Moskovich
Cc: freebsd-arch at freebsd.org
Subject: Re: FreeBSD spinlock - compatibility layer

On Tuesday, May 21, 2013 12:36:38 am Orit Moskovich wrote:
> That's not the case when using taskqueues for deferring  execution of 
> an
interrupt handler.
> Tasks can be delayed using the global taskqueue taskqueue_swi, which
executes its tasks in the context of an interrupt.
> In this case sleep is forbidden, and using spin mutex is not (although 
> might
be not recommended).

No, swi's run in an interrupt thread, and interrupt threads can use regular mutexes.  (That is why they run in a thread context.)  The only way you can run in a context requiring a spin lock in a driver is to use an interrupt filter.

--
John Baldwin