On Thu, 2010-03-04 at 19:51 +0530, James Bottomley wrote: > > Technically, he is. In the old days, most VI architectures were high > end enough not to require PIO transfers. The only exception was an > IDE driver used by sparc, which lead to the arch specific ide in/out > string instructions, in which sparc actually did all the necessary > flushing. Actually, Catalin's problem is with newer PIPT ARM :-) > So no other drivers than old IDE grew up with cache flushing in the > PIO case (and almost no high end VI hardware had an IDE interface, so > they rarely got implemented in the arch layer). However, recently, > with the transition from old IDE to libata and the prevalence of ARM > with more commodity hardware, the deficiency is becoming exposed. > Even the PA8000 workstations now come with an IDE CD, which means > we're starting to have problems with them as well. I don't think there's a core or driver problem in this specific case. As we discussed earlier, I believe the problem is that ARM considers a fresh page out of the page cache as "clean" instead of "dirty", and inverting that like we do on powerpc will fix their problem too. > > Seems like ARM has requirement other architectures do not, that is > > a) not documented anywhere > > b) causes problems > > > > You could argue that performance improvement (how big is it, > anyway?) > > is worth it, but this should be agreed to by wider community... > > Performance is always worth it provided we don't sacrifice > correctness. > The thing which was discovered in this thread is basically that ARM is > handling deferred flushing (for D/I coherency) in a slightly different > way from everyone else ... once that's fixed, ARM will likely not have > the D/I problem, but we'll still have the libata (and other PIO > systems) D flushing issue. You mean older VIVT ARM will grow a new issue there ? Cheers, Ben. -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
