Messages in this thread | | | From | Michael Buesch <> | Subject | Re: Opinion on ordering of writel vs. stores to RAM | Date | Sun, 10 Sep 2006 20:02:43 +0200 |
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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 >
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