Date: Fri, 30 Apr 2004 00:24:26 -0600 From: Scott Long <scottl@freebsd.org> To: "J.D. Bronson" <jbronson@wixb.com> Cc: freebsd-scsi@freebsd.org Subject: Re: AHC_ALLOW_MEMIO 5.2.1 Message-ID: <4091F11A.8010605@freebsd.org> In-Reply-To: <6.1.0.6.2.20040429063234.024493d8@localhost> References: <6.1.0.6.2.20040429063234.024493d8@localhost>
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J.D. Bronson wrote: > >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! > > Enable bootverbose. Scott
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