[Qemu-devel] DMA with Knoppix and qemu (cvs-version)

[Qemu-devel] DMA with Knoppix and qemu (cvs-version)

[Sven Köhler]

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Hi,

i just booted a recent knoppix-cd (4.0.2) and i'm trying to enable DMA,
but it won't work!

I started qemu with that command:

qemu -m 256 -cdrom knoppix.iso -boot d

But inside knoppix, a "hdparm -d1 /dev/hdc" won't work:
  HDIO_SET_DMA failed: Operation not permitted


Are there some issues with qemu's DMA support and Linux?
(qemu does have DMA support, doesn't it?)


Greetings
  Sven


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[Qemu-devel] Re: DMA with Knoppix and qemu (cvs-version)

[Sven Köhler]

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> i just booted a recent knoppix-cd (4.0.2) and i'm trying to enable DMA,
> but it won't work!
> 
> I started qemu with that command:
> 
> qemu -m 256 -cdrom knoppix.iso -boot d
> 
> But inside knoppix, a "hdparm -d1 /dev/hdc" won't work:
>   HDIO_SET_DMA failed: Operation not permitted

Ah ha! DMA mode work for harrdisks, but not for cdroms.

Strange - why?


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Re: [Qemu-devel] DMA with Knoppix and qemu (cvs-version)

[andrzej zaborowski]

Hi there,

On 05/05/06, Sven Köhler <skoehler@upb.de> wrote:
> Hi,
>
> i just booted a recent knoppix-cd (4.0.2) and i'm trying to enable DMA,
> but it won't work!
>
> I started qemu with that command:
>
> qemu -m 256 -cdrom knoppix.iso -boot d
>
> But inside knoppix, a "hdparm -d1 /dev/hdc" won't work:
>   HDIO_SET_DMA failed: Operation not permitted
>
Just a note: setting DMA through hdparm doesn't work on Linux since
tens of versions ago, it's been depreceted and you have to trust the
on-boot autodetection (and it works fine -- unless you didn't compile
the right driver in). It's the same on real machines.
>
> Are there some issues with qemu's DMA support and Linux?
> (qemu does have DMA support, doesn't it?)
>
>
> Greetings
>   Sven
>
>
>
> _______________________________________________
> Qemu-devel mailing list
> Qemu-devel@nongnu.org
> http://lists.nongnu.org/mailman/listinfo/qemu-devel
>
>
>
>

Regards,
Andrzej
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[Qemu-devel] Re: DMA with Knoppix and qemu (cvs-version)

[Sven Köhler]

> Just a note: setting DMA through hdparm doesn't work on Linux since
> tens of versions ago, it's been depreceted and you have to trust the
> on-boot autodetection (and it works fine -- unless you didn't compile
> the right driver in). It's the same on real machines.

WHAT!?

i have used it with Knoppix since ages. Knoppix has DMA disabled (for
some reason). Most of the time i boot knoppix with "dma" in the
append-line, but in the other cases, hdparm works and improves
performance dramatically.

Re: [Qemu-devel] DMA with Knoppix and qemu (cvs-version)

[andrzej zaborowski]

On 07/05/06, Jens Axboe <qemu@kernel.dk> wrote:
> On Sat, May 06 2006, andrzej zaborowski wrote:
> > Hi there,
> >
> > On 05/05/06, Sven Köhler <skoehler@upb.de> wrote:
> > >Hi,
> > >
> > >i just booted a recent knoppix-cd (4.0.2) and i'm trying to enable DMA,
> > >but it won't work!
> > >
> > >I started qemu with that command:
> > >
> > >qemu -m 256 -cdrom knoppix.iso -boot d
> > >
> > >But inside knoppix, a "hdparm -d1 /dev/hdc" won't work:
> > >  HDIO_SET_DMA failed: Operation not permitted
> > >
> > Just a note: setting DMA through hdparm doesn't work on Linux since
> > tens of versions ago, it's been depreceted and you have to trust the
> > on-boot autodetection (and it works fine -- unless you didn't compile
> > the right driver in). It's the same on real machines.
>
> Nonsense, hdparm -d1 is a perfectly valid way to enable DMA on PATA
> drives post boot.

Oops, right, the documentation confirms that. I don't know why I was
thinking that.
>
> --
> Jens Axboe
>
>

Regards,
Andrzej
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