From owner-freebsd-questions@FreeBSD.ORG Thu Nov 23 19:20:27 2006 Return-Path: X-Original-To: freebsd-questions@freebsd.org Delivered-To: freebsd-questions@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 66A2016A538 for ; Thu, 23 Nov 2006 19:20:27 +0000 (UTC) (envelope-from kris@obsecurity.org) Received: from elvis.mu.org (elvis.mu.org [192.203.228.196]) by mx1.FreeBSD.org (Postfix) with ESMTP id 7B03343D64 for ; Thu, 23 Nov 2006 19:19:50 +0000 (GMT) (envelope-from kris@obsecurity.org) Received: from obsecurity.dyndns.org (elvis.mu.org [192.203.228.196]) by elvis.mu.org (Postfix) with ESMTP id E52361A3C20; Thu, 23 Nov 2006 11:20:26 -0800 (PST) Received: by obsecurity.dyndns.org (Postfix, from userid 1000) id 1634451438; Thu, 23 Nov 2006 14:20:12 -0500 (EST) Date: Thu, 23 Nov 2006 14:20:11 -0500 From: Kris Kennaway To: Dieter Message-ID: <20061123192011.GA81772@xor.obsecurity.org> References: <20061123075214.GA51991@xor.obsecurity.org> <200611231735.RAA19097@sopwith.solgatos.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="Q68bSM7Ycu6FN28Q" Content-Disposition: inline In-Reply-To: <200611231735.RAA19097@sopwith.solgatos.com> User-Agent: Mutt/1.4.2.2i Cc: freebsd-questions@freebsd.org Subject: Re: processes not getting fair share of available disk I/O (was: Re: TCP parameters and interpreting tcpdump output ) X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 23 Nov 2006 19:20:27 -0000 --Q68bSM7Ycu6FN28Q Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Nov 23, 2006 at 09:35:08AM +0000, Dieter wrote: > > > > > hw.ata.wc=3D3D3D0 > > > > ^^^^^^^^^^^ > > > > "Make my hard drive go reeeeally slow please (just in case I crash)= " :) > > >=3D20 > > > Slower, yes, but not *that* slow. > > >=3D20 > > > Normal ls : 0.032 second. Two processes using same disk, multiply by= two, > > > so 0.064 second. Maybe the multiplier is more than 2, call it 10x, so > > > 0.32 second. But I'm seeing a factor of over 9100x. > >=20 > > Humour me and turn it back on, then see what happens. >=20 > Where is the knob to turn the write cache on/off on a per-drive basis > in FreeBSD? I can do this in NetBSD, but the only knob I can find in > FreeBSD affects all drives, and requires a reboot. Yes, I think you need to do it globally at boot time. > Humour me and read the Subject line. The ls does not get its fair share > of disk I/O. >=20 > Both times are with the disk's write cache in write-through mode. > I'm not comparing times with the write cache in different modes. > I'm comparing ls by itself against ls competing with cp. Your cp is going to be running synchronously, i.e. spend a lot of time waiting on the disk to perform the writes. This may well be the cause of your problem. Once we have established whether or not it is the cause, we can proceed to whether this behaviour can be improved. Kris --Q68bSM7Ycu6FN28Q Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.5 (FreeBSD) iD8DBQFFZfRrWry0BWjoQKURAmOMAKCeJjucWvpLHjlO6TOG/A9VC7ztRACg69SP pPINBxcReVcqFVTqjKrtGuY= =BQeY -----END PGP SIGNATURE----- --Q68bSM7Ycu6FN28Q--