Date: Thu, 29 Apr 2004 06:33:45 -0500 From: "J.D. Bronson" <jbronson@wixb.com> To: freebsd-scsi@freebsd.org Subject: Re: AHC_ALLOW_MEMIO 5.2.1 Message-ID: <6.1.0.6.2.20040429063234.024493d8@localhost>
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>Date: Wed, 28 Apr 2004 23:12:18 -0600 >From: Scott Long <scottl@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@speednet.com.au> >CC: "J.D. Bronson" <jbronson@wixb.com>, freebsd-scsi@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@aurora.org // Pager: 414.314.8282
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