Hi Zach!
Thanks for the responses.
--
On Tue, 2 Oct 2007, Zach Brown wrote:
>
> On Oct 1, 2007, at 1:39 PM, Peter Zijlstra wrote:
>
> >
> > On Mon, 2007-10-01 at 12:52 -0700, Zach Brown wrote:
> >
> >> Do you have any suggestions for locking constructs that RT would
> >> prefer?
> >
> > Basically, anything that maps to a simple mutex. Anything more complex
> > gets real messy real quick.
>
> I'm worried that the aio+dio implementation of concurrent pending IOs
> just doesn't map well to PI.
>
> Would a hack with a mutex and counts help at all? It seems like it
> would still have the same problem. The count increments don't
> transfer ownership to the count decrements and the wake up.
>
> io submission from tasks:
> down(&inode->i_mutex);
> atomic_inc(&inode->in_flight);
> up(&inode->i_mutex);
>
> io completion from interrupts:
> if(atomic_dec_and_test(&inode->in_flight))
> wake_up(&inode->waiting);
>
> file allocation in tasks:
> down(&inode->i_mutex);
> wait_event(inode->waiting, atomic_read(&inode->in_flight) == 0);
> up(&inode->i_mutex);
>
> (yeah, yeah, starvation -- it's just a demonstration)
This looks more like a completion. Actually, completions don't have PI
either, but they are usually OK.
>
> In any case, this seems like it's not a very high priority now that
> RT has Steven's work-around. If it does become a priority can you
> guys let linux-fsdevel know?
Actually, it may still be a high priority. We have one BUG currently that
seems to trigger starvation. But we don't know yet if it's a bug in the
test or in the FS code yet. I don't know the full details yet, but we do
have someone currently looking at it. These tests are what found this
issue in the first place.
When more info becomes available, I will definitely CC the linux-fsdevel
list. Thanks for letting me know about it. (I usually get confused by all
the different lists that are out there).
-- Steve
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