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Date: Sun, 9 Nov 1997 08:16:55 -0800 (PST)
From: rtm@eecs.harvard.edu
To: freebsd-gnats-submit@FreeBSD.ORG
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Subject: kern/4992: SCSI disk scheduling disabled in 2.2.5
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>Number:         4992
>Category:       kern
>Synopsis:       SCSI disk scheduling disabled in 2.2.5
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-bugs
>State:          open
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sun Nov  9 08:20:00 PST 1997
>Last-Modified:
>Originator:     Robert Morris
>Organization:
Harvard University
>Release:        2.2.5
>Environment:
FreeBSD frenulum.eecs.harvard.edu 2.2.5-RELEASE FreeBSD 2.2.5-RELEASE #1: Sat Nov  8 17:45:42 EST 1997     rtm@frenulum.eecs.harvard.edu:/amd/dominator/disk/glan25/kung/rtm/sys-2.2.5/compile/BOTH  i386
>Description:
The call to tqdisksort() in sd.c seems to be effectively commented
out by an #ifdef SDDISKSORT.

If one turns on SDDISKSORT, tqdisksort() still doesn't schedule
read requests, because of the "goto insert" early in the function.

Fixing all this improves my system's total throughput on heavy
multi-user loads by about 30% (when 20 processes are doing small
reads from different parts of the disk). With this load, scheduling
alone does slightly better than AHC_TAGENABLE by itself. Both
together improve performance by an additional 15%.
>How-To-Repeat:

>Fix:

>Audit-Trail:
>Unformatted: