Re: [RFC] Add support for semaphore-like structure with support for asynchronous I/O

[Suparna Bhattacharya <suparna@in.ibm.com>]

On Thu, Mar 31, 2005 at 08:22:17PM -0500, Trond Myklebust wrote:
> to den 31.03.2005 Klokka 16:13 (-0800) skreiv Andrew Morton:
> > Trond Myklebust <trondmy@trondhjem.org> wrote:
> > >
> > >  on den 30.03.2005 Klokka 18:17 (-0500) skreiv Trond Myklebust:
> > >  > > Or have I misunderstood the intent?  Some /* comments */ would be appropriate..
> > >  > 
> > >  > Will do.
> > > 
> > >  OK. Plenty of comments added that will hopefully clarify what is going
> > >  on and how to use the API. Also some cleanups of the code.
> > 
> > Ah, so that's what it does ;)
> > 
> > I guess once we have a caller in-tree we could merge this.  I wonder if
> > there's other existing code which should be converted to iosems.
> 
> I can put it into the NFS client stream which feeds into the -mm kernel.
> That will enable me to queue up the NFSv4 patches that depend on it
> too...
> 
> > You chose to not use the aio kernel threads?
> 
> I thought I'd do that in a separate patch since the aio workqueue is
> currently statically defined in aio.c.

I'll take a look at the patch over the weekend. I had a patch
for aio semaphores a long while back, but I need to spend some time
to understand how different this is.

Regards
Suparna

> 
> > Does iosem_lock_and_schedule_function() need locking?  It nonatomically
> > alters *lk_state.
> 
> iosem_lock_and_schedule_function() will always be called with the
> iosem->wait.lock held, since it is a waitqueue notification function.
> 
> In practice it is called by iosem_unlock(). The call to wake_up_locked()
> will trigger a call to __wake_up_common() which again tries the
> notification function of each waiter on the queue until it finds one
> that succeeds.
> 
> Cheers,
>   Trond
> 
> -- 
> Trond Myklebust <trond.myklebust@fys.uio.no>
> 
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-- 
Suparna Bhattacharya (suparna@in.ibm.com)
Linux Technology Center
IBM Software Lab, India