[RFC][CFT] GEOM direct dispatch and fine-grained CAM locking

[John Baldwin]

On Wednesday, September 04, 2013 10:11:28 am Nathan Whitehorn wrote:
> On 09/04/13 08:20, Ryan Stone wrote:
> > On Wed, Sep 4, 2013 at 8:45 AM, Nathan Whitehorn <nwhitehorn at freebsd.org> 
wrote:
> >> Could you describe what this macro is supposed to do so that we can do 
the
> >> porting work?
> >> -Nathan
> > #define GET_STACK_USAGE(total, used)
> >
> > GET_STACK_USAGE sets the variable passed in total to the total amount
> > of stack space available to the current thread.  used is set to the
> > amount of stack space currently used (this does not have to have
> > byte-precision).  Netgraph uses this to decide when to stop recursing
> > and instead defer to a work queue (to prevent stack overflow).  I
> > presume that Alexander is using it in a similar way.  It looks like
> > the amd64 version could be ported to other architectures quite easily
> > if you were to account for stacks that grow up and stacks that grow
> > down:
> >
> > 
http://svnweb.freebsd.org/base/head/sys/amd64/include/proc.h?revision=233291&view=markup
> >
> > /* Get the current kernel thread stack usage. */
> > #define GET_STACK_USAGE(total, used) do {                \
> >      struct thread    *td = curthread;                \
> >      (total) = td->td_kstack_pages * PAGE_SIZE;            \
> >      (used) = (char *)td->td_kstack +                \
> >          td->td_kstack_pages * PAGE_SIZE -                \
> >          (char *)&td;                        \
> > } while (0)
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> 
> I think that should be MI for us anyway. I'm not aware of any 
> architectures FreeBSD supports with stacks that grow up. I'll give it a 
> test on PPC.

ia64 has the double stack thingie where the register stack spills into a stack
that grows up rather than down.  Not sure how sparc64 window spills are 
handled either.

-- 
John Baldwin