On Sunday 10 September 2006 19:49, Linus Torvalds wrote:
>
> On Sun, 10 Sep 2006, Michael Buesch wrote:
> > >
> > > That's what IRIX had. It would let us get rid of mmiowb and avoid doing
> > > a full sync in writeX, so may be the best option.
> >
> > Last time I suggested that, people did not want it.
>
> I would personally _much_ rather have a separate mmiowb() and a regular
> spinlock, than add a magic new spinlock.
Yeah, as far as I remember it was you who rejected it. ;)
But I second your statement because of the practical issues below.
> Of course, mmiowb() itself is not a great name, and we could/should
> probably rename it to make it more obvious what the hell it is.
>
> > There is one little problem in practice with something
> > like spin_unlock_io().
> >
> > spin_lock_io(&lock);
> > foovalue = new_foovalue;
> > if (device_is_fooing)
> > writel(foovalue, REGISTER);
> > spin_unlock_io(&lock);
> >
> > That would be an unneccessary sync in case device is not fooing.
> > In contrast to the explicit version:
> >
> > spin_lock(&lock);
> > foovalue = new_foovalue;
> > if (device_is_fooing) {
> > writel(foovalue, REGISTER);
> > mmiowb();
> > }
> > spin_unlock(&lock);
>
> I think this is even more important when the actual IO is done somewhere
> totally different from the locking. It's really confusing if you have a
> "spin_unlock_io()" just because some routine you called wanted it.
>
> But more importantly, I don't want to have "spin_unlock_io[_xyzzy]()",
> where "xyzzy()" is all the irq/irqrestore/bh variations. It's just not
> worth it. We already have enough variations on spinlocks, but at least
> right now they are all in the "same category", ie it's all about what the
> context of the _locking_ is, and at least the lock matches the unlock, and
> there are no separate rules.
>
> Linus
>
--
Greetings Michael.
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