Re: Promise SX8 performance issues and CARM_MAX_Q

From: Matthew Collins
Date: Wed Mar 23 2005 - 18:27:58 EST


Jeff Garzik wrote:

Bernard Blackham wrote:

Hi,

Playing with a recently acquired Promise SX8 card, we've found
similar performance results to Matt's post to lkml a few months back
at http://marc.theaimsgroup.com/?l=linux-kernel&m=110175890323356&w=2

It appears that the driver is only submitting one command at a time
per port, which is at least one cause of the slowdowns. By raising
CARM_MAX_Q from 1 to 3 in drivers/block/sx8.c (it was 3 in an
earlier pre-merge incarnation of carmel.c), we're getting very
notable speed improvements, with no side effects just yet.

Knowing very little about what this change has actually done, I've a
few questions:
- Should this be considered dangerous?
- Why was it taken from 3 to 1?
- Is CARM_MAX_Q a number defined (or limited) by the hardware?


In multi-port stress tests, we couldn't get SX8 to function reliably without locking up or corrupting data, with more than one outstanding command.

Maybe a new firmware has solved this by now.

Jeff



Indeed there does seem to be new firmware out as of 2/23/05. I ran my tests with the 9/10/04 firmware but I did not adjust the CARM_MAX_Q value. Do either of you happen to know what firmware revisions you tested under?

I've put the machine with the SX8 controller into production despite the performance issues so I'm not going to be of any use for testing revisions to the driver :(

Matt
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