twa is giant locked in 7-Current or everywhere?

[Kris Kennaway]

On Wed, Aug 15, 2007 at 09:09:33PM +0400, Artem Kuchin wrote:
> Hi!
> 
> When i installed twas driver on 6.2-STABLE it said
> [FAST]
> 
> i presumed that it measn that twa is giant-lock free.
> 
> Now, after installing 7-CURRENT i see
> 
> Aug 15 17:00:02 omni3 kernel: 3ware device driver for 9000 series storage 
> controllers, version: 3.70.03.007
> Aug 15 17:00:02 omni3 kernel: twa0: <3ware 9000 series Storage Controller> 
> port 0x3000-0x30ff mem 0x88000000-0x89ffffff,0x8a200000-0x8a200fff irq 16 
> at devic
> Aug 15 17:00:02 omni3 kernel: twa0: [GIANT-LOCKED]
> Aug 15 17:00:02 omni3 kernel: twa0: [ITHREAD]
> 
> 
> So, it says GIANT-LOCKED and then ITHREAD.
> 
> Apparently, i have no real understaning what those words mean.
> COuld anyone explain the meaning of
> 
> FAST
> ITHREAD
> 
> Giant-locked is self explanatory and.. bad.

I think 6.x doesn't display the GIANT-LOCKED messages because users
were freaking out too much after they were added at an earlier point
in 6.x development ("Q: why is this driver suddenly giant locked?" "A:
It's always been giant locked, now this fact is displayed as a note to
developers.").

While it's true that a non-giant locked driver would be better, it's
not as bad as you might think because almost nothing else requires
giant for most workloads thesedays (see
http://wiki.freebsd.org/SMPTODO), so in those workloads performance
will not be worse because of it.  If you are really bothered by this
you can enable mutex profiling to check how much of a problem it is
for you.

Kris
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