disable TCQ?

disable TCQ?

[Michael Tokarev]

/sys/block/sdX/device/queue_depth file is read-write with
libsata, but is read-only with SCSI controllers  (at least
with the ones we have -- mostly aic7xxx or mptsas).

Googling for "disable tcq" gives results about {dis,en}abling
TCQ at boot time, and also mentions ipr (which we don't have).

Is there an option to control TCQ at runtime?

I'm doing a set of (pretty interesting) tests of various
drives and their TCQ/NCQ implementations, everything's
simple on SATA front but I can't test different TCQ modes
with SCSI drives because I can't find a way control TCQ
at runtime, and since those are production machines (I
plug/unplug spare drives for testing, but have no spare
machines), I can't reboot them often.

Thanks.

/mjt

Re: disable TCQ?

[Jeff Garzik]

Michael Tokarev wrote:
> /sys/block/sdX/device/queue_depth file is read-write with
> libsata, but is read-only with SCSI controllers  (at least
> with the ones we have -- mostly aic7xxx or mptsas).
> 
> Googling for "disable tcq" gives results about {dis,en}abling
> TCQ at boot time, and also mentions ipr (which we don't have).
> 
> Is there an option to control TCQ at runtime?

You have found the correct sysfs file -- but read/write access to it 
requires the SCSI driver to implement the ->change_queue_depth() hook.

'grep -w' will show that not too many drivers have implemented this yet, 
mostly the newer ones.  For older drivers, poke around and see if there 
is a driver-specific module option or somesuch.

	Jeff