Re: Playing with SATA NCQ

Jens Axboe
2005-05-29T19:08:06Z

On Sun, May 29 2005, Michael Thonke wrote:
> Jens Axboe schrieb:
>
> >There's really nothing to be tuned. If NCQ is enabled for your drive, it
> >will be printed in dmesg after the lba48 flag, such as:
> >
> >ata1: dev 0 ATA, max UDMA/133, 488281250 sectors lba48 ncq
> >
> >If you don't see NCQ there, your drive/controller doesn't support it.
> >Likewise you will have a queueing depth of > 1 if NCQ is enabled, check
> >/sys/block/sdX/device/queue_depth to see what the configured queueing
> >depth is for that device.
> >
> >
> >
> Hello again,
>
> the queue_depth of 30 is okay? On boot the CFQ scheduler tells:

By default, the maximum depth is used. For desktop use, a depth of 2-4
is probably more appropriate until the io schedulers become a little
more intelligent wrt queueing.

> cfq: depth 4 reached, tagging now on
>
> This only appears with AHCI enabled what does that mean?

It only appears if AHCI is enabled, because tagged command queueing is
only working/enabled on AHCI. The message is informational only, CFQ
tells you that it has detected queueing hardware (driver maintains a
depth of >= 4).

> Also a question which options can be set in queue_type?

Nothing.

--
Jens Axboe