AHC_ALLOW_MEMIO 5.2.1

[J.D. Bronson]

 >Date: Wed, 28 Apr 2004 23:12:18 -0600
 >From: Scott Long <scottl at freebsd.org>
 >User-Agent: Mozilla/5.0 (Macintosh; U; PPC Mac OS X Mach-O; en-US;
 >rv:1.7a) Gecko/20040214
 >To: Andy Farkas <andyf at speednet.com.au>
 >CC: "J.D. Bronson" <jbronson at wixb.com>, freebsd-scsi at freebsd.org
 >Subject: Re: AHC_ALLOW_MEMIO 5.2.1
 >
 >Andy Farkas wrote:
 >
 >>On Wed, 28 Apr 2004, J.D. Bronson wrote:
 >>
 >>>What happened to this kernel option on 5.2.1?
 >>>
 >>>AHC_ALLOW_MEMIO
 >>>
 >>>
 >>>It does not seem to be in any file at all anymore?
 >>>
 >>>  -JDB
 >>
 >>Its in /sys/conf/NOTES :)
 >>The generated file opt_aic7xxx.h will contain it.
 >>I sometimes enable this option in my kernels. Whether it does anything or
 >>not (performance-wise or other), I don't know.
 >
 >On x86, MEMIO is generally faster and causes the CPU to spin less than
 >IOPORT cycles do.  It can result in a minor but measurable speed
 >difference, though the effects of HyperThreading, when in use, could
 >offset the benefits.  In any case, the reason that this option exists
 >is to work around motherboards that incorrectly do write-combining on
 >MEMIO registers, something that most ahc/ahd chips do not support nor
 >handle well.  We added a somewhat sophisticated runtime test for this
 >to the driver last year, so there really isn't a reason to not enable
 >the option.  If you do and the test detects problems, it will
 >automatically throttle back to IOPORT.  We should probably just remove
 >the option all-together, and just use the sysctl/tunable as a backup in
 >case problems develope.
 >
 >Scott

Could it be possible to add a comment line to the driver so that if one 
enabled MEMIO, that dmesg could reflect that it was using MEMIO or not?

Right now, if I enable it - I cannot tell (to my knowledge) that it is 
working or not.

Thanks!





-- 
J.D. Bronson
Aurora Health Care // Information Services // Milwaukee, WI USA
Office: 414.978.8282 // Email: jd at aurora.org // Pager: 414.314.8282