Re: DMA disabled

[Florian Kulzer <florian@molphys.leidenuniv.nl>]

Sumith augustine wrote:
> Thanks a lot for responding
>
> On 3/23/06, Florian Kulzer <florian@molphys.leidenuniv.nl> wrote:
>
> > Sumith augustine wrote:
> >
> > > Hello Everybody,
> > >
> > > I am using a Sarge sys with Kernel 2.6.8-2-686 and Radi-1 (hda/hdc)
> > > Every day at boot time  am getting a DMA time out error for harddisk
> >
> > hdc,
> >
> > > it  says DMA is disabled. At the same time there is no problem with the
> >
> > hda.

[...]

> > > the hdparm results for hdc is
> > >
> > > /dev/hdc:
> > > multcount    =  0 (off)
> > > IO_support   =  0 (default 16-bit)
> > > unmaskirq    =  0 (off)
> > > using_dma    =  0 (off)
> > > keepsettings =  0 (off)
> > > readonly     =  0 (off)
> > > readahead    = 256 (on)
> > > geometry     = 65535/16/63, sectors = 78165360, start = 0

[...]

> hi Florian,
> As you asked am posting the lspci output :

[...]

> 0000:00:1f.1 IDE interface: Intel Corp. 82801DB/DBL (ICH4/ICH4-L)
> UltraATA-100 IDE Controller (rev 01)

To my knowledge, that controller is well supported by the "piix" module.
The fact that DMA works for hda suggests that all relevant modules are
loaded in the right order during boot. (You can list ide-related modules
with "lsmod|grep ide".) Therefore I am bit puzzled that it does not work
for hdc. You could check if there is a setting in the BIOS which would
interfere with it. (I think this is unlikely.) You could also try to
configure that second HD as the primary slave (hdb) instead of secondary
master. I think this will make it use the same IRQ as hda, which would
help if your problem is due to an IRQ conflict.

I think you can try to enable DMA yourself with hdparm and see if you
get an error message. If you want to be on the safe side you can boot
into single user mode and mount the drive read-only, or you could give
Knoppix a try.

[...]

> am using this machine as a webserver in my office and at times the client
> users say that the webserver is very slow. It is not slow always but  ll go
> slow for a while. Is this due to the disabled DMA ?...
> Let me tell this also am only a beginer ;-)

Your webserver probably caches pages in memory. This will mean fast
access when someone requests a page which has already been requested
before, and very slow access if the server has to load the page from the
HD. Therefore I think the lack of DMA can indeed explain this behavior.

Regards,
           Florian