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Date:      Wed, 26 Apr 2000 13:51:11 -0500
From:      Dan Nelson <dnelson@emsphone.com>
To:        Kent Stewart <kstewart@3-cities.com>
Cc:        Matthew Dillon <dillon@apollo.backplane.com>, Narvi <narvi@haldjas.folklore.ee>, Michael Bacarella <mbac@nyct.net>, Alfred Perlstein <bright@wintelcom.net>, Kevin Day <toasty@dragondata.com>, hackers@FreeBSD.ORG
Subject:   Re: Double buffered cp(1)
Message-ID:  <20000426135111.A21368@dan.emsphone.com>
In-Reply-To: <39073655.56A70C00@3-cities.com>; from "Kent Stewart" on Wed Apr 26 11:32:53 GMT 2000
References:  <Pine.BSF.3.96.1000426165333.74116e-100000@haldjas.folklore.ee> <3907177C.5CFEC69A@3-cities.com> <200004261751.KAA96154@apollo.backplane.com> <39073655.56A70C00@3-cities.com>

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In the last episode (Apr 26), Kent Stewart said:
> I just noticed that mine isn't showing "Tagged Queueing Enabled" is
> that something I can set? The adapter is an Adaptec 2940uw.
> 
> da0 at ahc0 bus 0 target 4 lun 0
> da0: <IBM DCAS-34330W S65A> Fixed Direct Access SCSI-2 device
> da0: 40.000MB/s transfers (20.000MHz, offset 8, 16bit)
> da0: 4134MB (8467200 512 byte sectors: 255H 63S/T 527C)

The CAM code has a quirk entry for IBM DCAS drives that turns it off;
check out /sys/cam/cam_xpt.c, line 320.  I suggest benchmarking with
and without the quirk entry, and if it's faster with tagged queueing,
update PR kern/10398.

-- 
	Dan Nelson
	dnelson@emsphone.com


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