investigation of Giant usage in kernel

[Kris Kennaway]

On Sun, Mar 04, 2007 at 06:55:50PM +0100, Ed Schouten wrote:
> Hello,
> 
> I took a grep on the kernel source and took a look to Giant usage as
> well. I too have a question about locking in uipc_domain.c:
> 
> The file has a mutex, dom_mtx, which protects the 'domain list lock',
> which could be declared static by the way. The strange thing is that it
> isn't used to lock the domain list lock in any way. It is only used to
> lock the domain_init_status variable. Wouldn't it be better to rename it
> to something better?
> 
> The pf_proto_register() routine locks and unlocks Giant. It looks like
> s/Giant/dom_mtx/ would be enough to remove the usage of Giant from
> uipc_domain.c.

This one doesn't seem to be a big deal because protocol registration
is unlikely to happen in a critical path.  i.e. a one-time Giant
acquisition is completely irrelevant, it's the acquisitions that might
happen hundreds or thousands of times a second in certain operational
conditions that matter.

I have updated the wiki with what seems to be a more or less complete
list of the remaining Giant instances in the kernel:

  http://wiki.freebsd.org/SMPTODO

Apart from some subsystems (ttys are the main one), and excluding the
items that are being actively worked on (e.g. CAM), there is not much
Giant left.

Kris
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