Hi!
> > > Which shouldn't be true. There is no fundamental reason why
> > > ordinary writes should be slower than O_DIRECT.
> >
> > Again, there IS a reason: O_DIRECT eliminates the cpu overhead of the
> > kernel-user copy,
>
> You assume that ordinary read()/write() is *required* to do the copying.
> It doesn't. Kernel is allowed to do direct DMAing in this case too.
Kernel is allowed, but it is practically impossible to code. It would
require slow MMU magic.
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
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http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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