I/O or Threading Suffer

[Mark Murray]

Robert Watson writes:
> > I'm sure it could. There are some Giant issues related to the UIO stuff
> > that bit me in the bum when I removed the NEEDS_GIANT flag from the
> > device, but I'm reasonably sure that with careful work this can be
> > untangled. 
> 
> UIO shouldn't require Giant.  Are you sure it still does?

EMEMORY

It was an issue over (t)sleeping with(out?) a lock held, and replacing
the tsleep with a msleep+mutex gave another problem where uiomove() was
called with(out?) a mutex held and that was Very Bad(tm).

Warner and PHK knew why it was bad; I'm hazy on details.

>                               Are you sure it still does?  FYI, I'm not
> even thinking you have to mark the whole device driver as not requiring
> Giant, just dropping Giant about some of the long running work (and maybe
> conditional on the amount of work).  For a small random read, it's not
> worth it, but for sustained large reads of randomness, it might be
> interesting to see what impact it has.  We could even consider a yield of
> some sort.

That sounds easy enough. It may take me a bit of time to get a machine
stable enough for testing. Please nag!

> Anyhow, up front, it might be sufficient to drop and reacquire giant and
> see what impact it has for the test scenario we're currently looking at.

Sure. Modulo instability, I'll do it ASAP.

M
--
Mark Murray
iumop ap!sdn w,I idlaH