Date: Fri, 5 Mar 1999 11:00:01 -0800 (PST) From: "Kenneth D. Merry" <ken@plutotech.com> To: freebsd-bugs@FreeBSD.org Subject: Re: kern/10398: Tagged queueing makes IBM DCAS-34330 slow Message-ID: <199903051900.LAA68391@freefall.freebsd.org>
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The following reply was made to PR kern/10398; it has been noted by GNATS.
From: "Kenneth D. Merry" <ken@plutotech.com>
To: hokada@isl.melco.co.jp
Cc: freebsd-gnats-submit@FreeBSD.ORG
Subject: Re: kern/10398: Tagged queueing makes IBM DCAS-34330 slow
Date: Fri, 5 Mar 1999 11:53:43 -0700 (MST)
hokada@isl.melco.co.jp wrote...
>
> >Number: 10398
> >Category: kern
> >Synopsis: Tagged queueing makes IBM DCAS-34330 slow
> >Confidential: no
> >Severity: serious
> >Priority: medium
> >Responsible: freebsd-bugs
> >State: open
> >Quarter:
> >Keywords:
> >Date-Required:
> >Class: change-request
> >Submitter-Id: current-users
> >Arrival-Date: Fri Mar 5 03:00:01 PST 1999
> >Closed-Date:
> >Last-Modified:
> >Originator: Hideaki Okada
> >Release: 3.1-RELEASE
> >Organization:
> MITSUBISHI Electric
> >Environment:
> FreeBSD waikiki.isl.melco.co.jp 3.1-RELEASE FreeBSD 3.1-RELEASE #5: Sat Feb 20 01:25:27 JST 1999 hokada@waikiki.isl.melco.co.jp:/usr/src/sys/compile/WAIKIKI i386
>
> >Description:
> My IBM DCAS-34330 hard drive is connected to Adaptec AHA-2940 adapter,
> and I found write performance is low.
> Simple throughput measurement like 'dd if=/dev/zero of=test bs=64k count=1000'
> shows ahout 3MB/s even though it should be 7-8MB/s .
> However, there is no trouble on read performance.
> Here is bonnie's results:
>
> -------Sequential Output-------- ---Sequential Input-- --Random--
> -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
> Machine MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU /sec %CPU
> 2.2.8R 100 6677 83.1 7542 22.8 3313 11.3 8519 93.4 7813 14.0 250.0 4.9
> 3.1R 100 7269 90.7 3199 10.5 2283 8.7 7450 95.7 7548 15.0 262.5 5.4
> 3.1R(*) 100 7376 91.3 6823 21.5 2628 9.3 6931 88.7 7469 14.3 240.6 4.7
>
> (*) tagged queuing is turned off by modifying cam_xpt.c
>
> >How-To-Repeat:
> I reported this on FreeBSD-users-jp@jp.freebsd.org mailing list,
> and the other report on this problem is posted.
> Its configuration is:
> IBM DCAS-34330W connected to AHA-2940UW
>
> >Fix:
> I put initializer of xpt_quirk_table at cam_xpt.c, and I got bonnie's result as reported above.
>
> {
> /*
> * Slow when tagged queueing is enabled. (3MB/sec versus
> * 8MB/sec.)
> */
> { T_DIRECT, SIP_MEDIA_FIXED, "IBM", "DCAS-34330", "S65A" },
> /*quirks*/0, /*mintags*/0, /*maxtags*/0
> },
Thanks for reporting this.
I would like to get some more information on the problem, though, before
disabling tagged queueing altogether for this drive. I have found that
some drives behave differently depending on whether or not write caching is
turned on. Also, it may be that we don't have to disable tagged queueing
completely, but just limit the number of tags to some low number.
The Seagate Medalist Pro is a good example of that. It has horrible write
performance when the number of tags is >= 3. But, at 2 tags or just 1
(i.e. tagged queueing disabled), its write performance is just fine.
So, the first thing to try is your bonnie test above, with write caching
enabled and with write caching disabled.
To see if write caching is enabled or disabled, do something like this:
camcontrol modepage -n da -u 4 -v -m 8
Look at the 'WCE' (Write Cache Enable) bit. If it is 1, write caching is
enabled. If it is 0, write caching is disabled. To change the value:
camcontrol modepage -n da -u 4 -v -m 8 -e -P 3
Obviously, if your disk is not da4, you'll need to change the -u argument
above to the unit number for your disk.
The next thing to try is to change the number of tags on the fly and
try to determine whether there is a point where performance drops off
completely.
I will send you some patches to camcontrol in private email that will allow
you to change the number of tags on the fly, and disable tagged queueing
altogether.
Ken
--
Kenneth Merry
ken@plutotech.com
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