[mythtv-users] Enable DMA
jonner at teegra.net
Fri Mar 23 12:26:23 UTC 2007
John Drescher wrote:
> On 3/23/07, Mitch Gore <mitchell.gore at gmail.com> wrote:
>> if i do that i get this...
>> [root at Mitchell_mc myth]# /sbin/hdparm -d1 /dev/sda
>> setting using_dma to 1 (on)
>> HDIO_SET_DMA failed: Inappropriate ioctl for device
> In most cases DMA is already on for sata devices and you can not
> enable it via the hdparm program.
Yes, I believe the reason for the error is that the ioctl to set DMA
mode on an SATA isn't implemented because it doesn't need to be. Any
proper driver for an SATA interface handles DMA mode internally (if it
needs to be handled at all), since DMA is a required part of the SATA
standard. Of course, some SATA interfaces present themselves as legacy
ATA interaces, so I don't know what would happen if you used Linux's
traditional ATA driver for one of those. You would know that this was
the case if the drive was called hd?, but yours is sda, so it's not.
I haven't needed to do anything related to DMA with VIA SATA interfaces
and sata-via. One way to tell if a drive is not using DMA is to watch
the CPU load with top or something while using the disk heavily, such as
copying a large file. If there is high system or user CPU load and the
system feels sluggish, DMA mode may not be set.
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