[2932] in linux-scsi channel archive
DPT 2044U and Quantum Fireball ST4.3
daemon@ATHENA.MIT.EDU (Dario_Ballabio)
Tue Dec 16 06:03:50 1997
Date: Tue, 16 Dec 1997 11:51:26 +0100
From: Dario_Ballabio@milano.europe.dg.com (Dario_Ballabio)
To: linux-scsi@vger.rutgers.edu
You must limit the number of scsi commands queued to your disk drive.
In your case you shoud use the EATA ISA/EISA/PCI driver and either
set the compile option "maximum number of queued commands" or
the boot option "eata=mq:xx" to a suitable value.
In your case it looks like 8 is a good value to start with.
If you do not specify the max queue value, the driver uses its
own algotithm, which allocates the max number of outstanding
commands to the controller (64) among the various scsi devices.
For detalis just look at the select_queue_depths routine in eata.c,
which is small and not difficult to read.
When tagging is enabled at the dpt bios level, you need not set
the "tagged command queuing" (or tc:y) option.
About elevator sorting, I do not know any circumstance in which
it could be useful to turn it off.
The select_queue_depths implementation works as expected only when
the scsi devices are sized at driver initialization, not when they
are sized at a later time. This is a limitation of the actual scsi
code and holds true for all scsi drivers.
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