advocacy/73642: More AHC_ALLOW_MEMIO

Wei-Kai Wu wkwu at
Sun Nov 7 07:40:28 PST 2004

>Number:         73642
>Category:       advocacy
>Synopsis:       More AHC_ALLOW_MEMIO
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    freebsd-advocacy
>State:          open
>Class:          change-request
>Submitter-Id:   current-users
>Arrival-Date:   Sun Nov 07 15:40:27 GMT 2004
>Originator:     Wei-Kai Wu
>Release:        FreeBSD 4.10-STABLE i386
System: FreeBSD 4.X-Series , 5.X-Series
The adaptec SCSI controller such as Aic7892 (29160 SCSI adapter) uses "ahc"
driver which has an option "AHC_ALLOW_MEMIO".
The AHC_ALLOW_MEMIO enhances the I/O performance a lot compared with those 
SCSI drivers have no MEMIO option.
I have tried Adaptec AIC7902 Ultra320 SCSI adapter (which has no MEMIO option),
and the performance is really bad compared with Aic7892 MEMIO option.
I doubt why there is no MEMIO option for other SCSI controllers?

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