Re: How do I enable UDMA automatically

[Joe Cooper <joe swelltech com>]

Kalum Somaratna aka Grendel wrote:
> 
> Greetings,
> 
> The kernel doesn't seem to use DMA, although i did indeed compile my
> kernel with enable DMA access for the HDD set to on, it doesn't use it by
> default...as seen with the hdparm program...
> /sbin/hdparm /dev/hda
> 
> /dev/hda:
>  multcount    =  0 (off)
>  I/O support  =  0 (default 16-bit)
>  unmaskirq    =  0 (off)
>  using_dma    =  0 (off)
>  keepsettings =  0 (off)
>  nowerr       =  0 (off)
>  readonly     =  0 (off)
>  readahead    =  8 (on)
>  geometry     = 1582/255/63, sectors = 25429824, start = 0
> 
> thses are the default settings, as you can see it is way inefficient,UDMA
> is off, I/O support is 16 bit...and see the ratings for the test run with
> 
> hdparm -t -T  /dev/hda
> 
> /dev/hda:
>  Timing buffer-cache reads:   64 MB in  0.48 seconds =133.33 MB/sec
>  Timing buffered disk reads:  32 MB in  7.38 seconds = 4.34 MB/sec
> 
> watch the buffered disk reads rating....
> 
> now I enable dma using -d1 and just see the difference
> 
> /sbin/hdparm -d1 /dev/hda
> 
> now I run the same test
> 
> /dev/hda:
>  Timing buffer-cache reads:   64 MB in  0.43 seconds =148.84 MB/sec
>  Timing buffered disk reads:  32 MB in  2.31 seconds =13.85 MB/sec
> 
> see when the dma is enabled it is 3 times faster!!!!
> 
> So what I want to ask is how to enable dma by default, should I put the
> command in the inittab...???

Nope.  /etc/rc.d/rc.local is what you want.  Put it as the last command.

Another option is to recompile your kernel and choose "Use DMA by
Default", or something like that, when configuring.

                                 -- 
                    Joe Cooper <joe swelltech com>
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