Re: [Qemu-devel] enabling bus-master IDE driver

[Jason Brittain <jason@brittainweb.org>]

zitu wrote:
> Quoting zitu <zitu@free.fr>:
> 
>>>Does that mean that the patch doesn't work?  Do I have to do something else
>>>to make dma work?
>>
>>I think this patch is almost complete for linux and solaris guests. Some
>>more work/init is needed inside XP/NT/2K. Anyone around with this
>>knowledge ?
> 
> answering to myself... :)
> 
> WIN_WRITEDMA_EXT & WIN_READDMA_EXT cases are not defined in hw/ide.c
> I have no idea where to start to write a patch for these... :(
> 
> Until these and the atapi_dma are set/defined, no dma should work IMHO.
> And this seems not to be OS dependant.
> 
> Which means the linux figures I got were wrong ???

My Linux (kernel 2.6) guest's disk seems slow too.  I applied the DMA
patch, and at first it seemed faster (it may be a bit faster).  But,
I tried using hdparm -d1 /dev/hda to make sure DMA was turned on in
the guest Linux and it said:

/dev/hda:
  setting using_dma to 1 (on)
  HDIO_SET_DMA failed: Operation not permitted
  using_dma    =  0 (off)

So I'm pretty sure DMA doesn't work with this patch even with a Linux
guest -- at least in my setup.

-- 
Jason Brittain