From owner-freebsd-fs  Thu Sep 21  8: 0:12 2000
Delivered-To: freebsd-fs@freebsd.org
Received: from freebsd.dk (freebsd.dk [212.242.42.178])
	by hub.freebsd.org (Postfix) with ESMTP
	id 6F4AB37B424; Thu, 21 Sep 2000 08:00:06 -0700 (PDT)
Received: (from sos@localhost)
	by freebsd.dk (8.9.3/8.9.1) id RAA92422;
	Thu, 21 Sep 2000 17:02:58 +0200 (CEST)
	(envelope-from sos)
From: Soren Schmidt <sos@freebsd.dk>
Message-Id: <200009211502.RAA92422@freebsd.dk>
Subject: Re: disable write caching with softupdates?
In-Reply-To: <8133266FE373D11190CD00805FA768BF055BD1D6@shrcmsg1.tdh.qntm.com> from Stephen Byan at "Sep 21, 2000 07:08:37 am"
To: Stephen.Byan@quantum.com (Stephen Byan)
Date: Thu, 21 Sep 2000 17:02:57 +0200 (CEST)
Cc: mbendiks@eunet.no ('Marius Bendiksen'), fs@FreeBSD.ORG,
	sos@FreeBSD.ORG, freeBSD-scsi@FreeBSD.ORG
X-Mailer: ELM [version 2.4ME+ PL54 (25)]
MIME-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 8bit
Sender: owner-freebsd-fs@FreeBSD.ORG
Precedence: bulk
X-Loop: FreeBSD.org

It seems Stephen Byan wrote:
> Marius Bendiksen [mailto:mbendiks@eunet.no] wrote:
> 
> > > Contrast this 10% performance hit versus what you get when 
> > you disable
> > > caching entirely.
> > 
> > I think you will see that on some drives, this may have a greater
> > performance impact than not caching at all.
> 
> Perhaps Søren will be kind enough to run the experiment? I'd be interested
> in analyzing cases in ATA drives where flushing delivers worse performance
> than disabling cache.

Well, I have been toying a bit with this, so far results are just
timing of a make -j16 buildworld on two IBM DJNA drives (ie no tags)
with varius setups.

ATA driver "as is":
3602.63 real         0.00 user      2865.62 sys

ATA driver with flush cache on "BIO_ORDERED":
3964.18 real         0.00 user      2870.09 sys

ATA driver with write cache disabled:
4423.30 real         0.00 user      2871.87 sys

So, having the write cache there definitly is a win.

I'll try this on TWO IBM DTLA drives with tags enabled and see what gives..

Anything else you want me to mess with now we are at it ?

-Søren


To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-fs" in the body of the message