Re: 2.1.111: IDE DMA disabled...BLAH...BLAH...

Linus Torvalds (
Wed, 29 Jul 1998 11:01:35 -0700 (PDT)

On Wed, 29 Jul 1998, Alan Cox wrote:
> Linus - Yes there is something wrong
> No it cannot be DMA if DMA goes back to 1.3.20, almost every report
> says it started in 2.1.x, most are not UDMA but older DMA

Sure it can be DMA. We're doing a lot of things differently, and it's
entirely conceivable that timings just changed for the worse (or better,
depending on how you look at it).

Easy to test, in fact - run bonnie on 2.0.x and a later 2.1.x, and look at
the numbers. If they're consistently different one way or the other it
means that we're hitting the disk subsystem harder/less hard.

> The only common theme right now seems to be SMP and SCSI, and thats SMP
> machines in the SCSI case (not option), unknown in the IDE case.

Which may well be that there is a problem with cache timings or something.
One thing that is new in 2.1.x is that we're a _lot_ more parallell, for
example. Another difference is that we react to interrupts a lot faster
under SMP.


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