From owner-freebsd-current@FreeBSD.ORG Mon Mar 4 08:38:17 2013 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by hub.freebsd.org (Postfix) with ESMTP id A36E2896; Mon, 4 Mar 2013 08:38:17 +0000 (UTC) (envelope-from peter@rulingia.com) Received: from vps.rulingia.com (host-122-100-2-194.octopus.com.au [122.100.2.194]) by mx1.freebsd.org (Postfix) with ESMTP id 3EBFB65D; Mon, 4 Mar 2013 08:38:16 +0000 (UTC) Received: from server.rulingia.com (c220-239-237-213.belrs5.nsw.optusnet.com.au [220.239.237.213]) by vps.rulingia.com (8.14.5/8.14.5) with ESMTP id r248c7u7034504 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK); Mon, 4 Mar 2013 19:38:08 +1100 (EST) (envelope-from peter@rulingia.com) X-Bogosity: Ham, spamicity=0.000000 Received: from server.rulingia.com (localhost.rulingia.com [127.0.0.1]) by server.rulingia.com (8.14.5/8.14.5) with ESMTP id r248c2HL045173 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Mon, 4 Mar 2013 19:38:03 +1100 (EST) (envelope-from peter@server.rulingia.com) Received: (from peter@localhost) by server.rulingia.com (8.14.5/8.14.5/Submit) id r248c2Of045172; Mon, 4 Mar 2013 19:38:02 +1100 (EST) (envelope-from peter) Date: Mon, 4 Mar 2013 19:38:02 +1100 From: Peter Jeremy To: Don Lewis Subject: Re: access to hard drives is "blocked" by writes to a flash drive Message-ID: <20130304083802.GA44865@server.rulingia.com> References: <20130304053547.GY2930@kib.kiev.ua> <201303040712.r247CejP008718@gw.catspoiler.org> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="3MwIy2ne0vdjdPXF" Content-Disposition: inline In-Reply-To: <201303040712.r247CejP008718@gw.catspoiler.org> X-PGP-Key: http://www.rulingia.com/keys/peter.pgp User-Agent: Mutt/1.5.21 (2010-09-15) Cc: freebsd-current@freebsd.org X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 04 Mar 2013 08:38:17 -0000 --3MwIy2ne0vdjdPXF Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2013-Mar-03 23:12:40 -0800, Don Lewis wrote: >On 4 Mar, Konstantin Belousov wrote: >> It could be argued that the current typical value of 16MB for the >> hirunningbufspace is too low, but experiments with increasing it did >> not provided any measureable change in the throughput or latency for >> some loads. > >The correct value is probably proportional to the write bandwidth >available. The problem is that write bandwidth varies widely depending on the workload. For spinning rust, this will vary between maybe 64KBps (512B random writes) and 100-150MBps (single-theaded large sequential writes). The (low-end) SSD in my Netbook also has about 100:1 variance due to erase blocking. How do you tune hirunningbufspace in the face of 2 or 3 orders of magnitude variance in throughput? Especially since SSDs don't gradually degrade - they hit a brick wall. --=20 Peter Jeremy --3MwIy2ne0vdjdPXF Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.19 (FreeBSD) iEYEARECAAYFAlE0XWoACgkQ/opHv/APuIeHbACcCk/rPZvdWOaw39O04JSSk131 WZsAn1uwrzYpq9e+yPGGdfsz6a4rtRuC =MVQ7 -----END PGP SIGNATURE----- --3MwIy2ne0vdjdPXF--