Slackware Optical Drive DMA?

linuxbird · 07-28-2014, 10:39 PM

First, finding posts on DMA is tough because the search engine appears to not search on short terms.

Second, I am using Slackware 14.1 on my systems.

Here's the problem....apparently the optical drive does not come up as a DMA device. This can be a problem when booting off optical, but it is a bigger issue if frequent backups are done via the optical drive.

I am open to any suggestions as to how to proceed in understanding this issue.

It would be very good to have optical drive IO done via DMA.

Thanks for any pointers.

business_kid · 07-29-2014, 04:34 AM

The first thing I would try is a session with hdparm on the drive investigating. Does it do dma? does that improve the read times. man hdparm for options. hdparm -i and -I are interesting. Mine says SATA ≤ 3.0, udma ≤ 5, and ATA/ATAPI ≤7, and that's a recent drive. You should not get higher than ata ≥ 4 without DMA.

So it may not say dma, but if it's running a fast mode it's doing it.

onebuck · 07-29-2014, 08:16 AM

Hi,

Getting information directly from '/dev/sr0' via 'hdparm -I /dev/sr0' shows;

Quote:

~# hdparm -I /dev/sr0

/dev/sr0:

ATAPI CD-ROM, with removable media
Model Number: HL-DT-STDVD+/-RW GT32N
Serial Number: KZ1B74B3743
Firmware Revision: A203
Transport: 0x7200; Revision: 0x5356
Standards:
Likely used CD-ROM ATAPI-1
Configuration:
DRQ response: 50us.
Packet size: 12 bytes
cache/buffer size = unknown
Capabilities:
LBA, IORDY(can be disabled)
DMA: sdma0 sdma1 sdma2 mdma0 mdma1 mdma2 udma0 udma1 udma2 udma3 udma4 *udma5
Cycle time: min=120ns recommended=120ns
PIO: pio0 pio1 pio2 pio3 pio4
Cycle time: no flow control=120ns IORDY flow control=120ns

So my device is udma5 capable.

From 'man hdparm';

Quote:

-I Request identification info directly from the drive, which is displayed in a new expanded format with considerably more detail than with the
older -i option.

Hope this helps.
Have fun & enjoy!

dugan · 07-29-2014, 11:18 AM

Isn't DMA automatically turned on for SATA drives?

Why do you think DMA isn't turned on for your optical drive?

business_kid · 07-29-2014, 01:02 PM

Is yours a PATA device = on an old style ide ribbon?
If so, make sure the ribbon is 80 way, and not 40way. The extra lines are earths to stop cross talk.

linuxbird · 07-30-2014, 09:26 AM

Thanks for all the replies.

I get similar results from hdparm. Just because it is capable, doesn't mean that DMA is on. So if I do hdparm -d 1 /dev/sr0, I am told that DMA failed.

The instant machine is a SATA drive, but I note similar on an IDE drive on a different system.

I believe what is happening is that DMA is never activated, even for the SATA drive, at system start.

I also believe that PIO is probably fast enough for the drive, but DMA might incur less overhead on large transfers.

business_kid · 07-30-2014, 10:46 AM

I think you are right. It doesn't actually matter a hoot on the cd. The disk surface seems to affect read speeds more than anything else. read speeds are all ≤ 3MB/S here with various cds, cdrs curiously being faster than pressed disks.

The sata drive will make a difference if it is not dma. Usually it loses dma because it has been grabbed by the wrong driver, and this was a principal reason for me building my own kernel in days gone by.