AHC_ALLOW_MEMIO 5.2.1

[Scott Long]

J.D. Bronson wrote:
>  >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!
> 
> 

Enable bootverbose.

Scott