Subject: Re: splusb()
To: Garrett D'Amore <firstname.lastname@example.org>
From: SODA Noriyuki <email@example.com>
Date: 05/05/2006 16:28:30
>>>>> On Thu, 04 May 2006 10:27:04 -0700,
"Garrett D'Amore" <firstname.lastname@example.org> said:
> The splxxx stuff is single processor legacy from the idea that you could
> just set the processor mask and that this was sufficient.
> If we want to support true kernel SMP ever, then we need to go to
> mutexes or something like them.
That depends on what "proper" means. :)
spl + spinclock can be used to support fine grained SMP system too,
just like what is written in Curt Schimmel's "UNIX Systems for Modern
Architectures: Symmetric Multiprocessing and Caching for Kernel
> As far as performance goes, mutexes are not likely to be very different
> if design so that on uni processor platforms acquiring a mutex that has
> an "interrupt cookie" set for it (i.e. a mutex that protects data
> accessed in an ISR) degenerates into just doing the splxxx thing
Yes. The problem is that FreeBSD and Solaris treat interrupt handlers
as threads, thus the handling is more expensive.
The threading model itself is beautiful, though.