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Re: Knoppix dma (Re: [vox-tech] X crash, Mozilla)
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Re: Knoppix dma (Re: [vox-tech] X crash, Mozilla)

On Thu 22 Jul 04,  9:09 AM, Jonathan Stickel <jjstickel@sbcglobal.net> said:
> Mark K. Kim wrote:
> >On Wed, 21 Jul 2004, Jonathan Stickel wrote:
> >
> >
> >>Not sure why, but Knoppix doesn't use dma by default for ide devices;
> >>maybe because old hardware doesn't support dma and will hang.
> >
> >
> >Umm... are you sure?  I think it does not enable DMA only if it doesn't
> >recognize the IDE controller as one that supports DMA.  That's the default
> >behavior for Debian, RedHat, and Mandrake also.
> >
> I'm very sure.  At least that's what I've found using Knoppix on several 
> "new" computers (>1ghz).  I have to enter "knoppix dma" or I get no dma 
> and it's very slow.  You can see the dma option (and others) by pushing 
> F2 at the boot prompt.
> And it is surprising because I know DMA is on by default in all major 
> distributions and other linux boot cds I've tried.
> Jonathan

this says that dma is not enabled by default ever:


Q: Why is DMA disabled by default and how do i enable it 

A: Some chipsets and/or harddiscs are broken or buggy. Using DMA would
cause problems on such systems. If your system works properly with DMA,
you can enable it with it by typing "/sbin/hdparm -c3 -d1 -m16 -k1
/dev/hda" or by editing the "/etc/init.d/bootmisc.sh" startup script and
uncommenting the hdparm -qd1 /dev/hda line to have it permanently on at
reboot, if the line is not there add it. Read more:

this says that dma is enabled once the kernel boots:


After spending quite some time understanding the knoppix boot sequence,
it seems that DMA is not enabled for initrd & loading vmlinuz!!! And I'm
not sure whether initrd is doing anything really useful. Remove it from
lilo and be happy. DMA is enabled at only a very late stage. So I should
still expect a major speedup once I know how to enable DMA from the very

perhaps the only time the system is certain to have dma enabled is when
the system is in an eigenstate of the dma operator?


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