Messages in this thread | | | Date | Tue, 6 Feb 2007 20:39:15 +0000 | From | Pavel Machek <> | Subject | Re: O_DIRECT question |
| |
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 (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |