From owner-svn-src-head@freebsd.org Fri Oct 16 19:22:55 2015 Return-Path: Delivered-To: svn-src-head@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id C103BA16A3F for ; Fri, 16 Oct 2015 19:22:55 +0000 (UTC) (envelope-from imp@bsdimp.com) Received: from mail-pa0-f42.google.com (mail-pa0-f42.google.com [209.85.220.42]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 8F4EE1FC2 for ; Fri, 16 Oct 2015 19:22:55 +0000 (UTC) (envelope-from imp@bsdimp.com) Received: by pacez2 with SMTP id ez2so12460628pac.1 for ; Fri, 16 Oct 2015 12:22:49 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:sender:subject:mime-version:content-type:from :in-reply-to:date:cc:message-id:references:to; bh=/NPcPuaCR0MBkXgogxlgeGuh06z3sAqTUZJSoeEIAiI=; b=WpyU4KD50KFqcE9WAhjGcyqNlANLhIIbuA9PmStxJl+A+urY3OLkTS04ZyPFm/EQpk ds686eNDQJLlXEu6HUN9ac9bry/2qltLrEZlDAf33/Ztrt9EkgXCp3mLio3eOYIsZs2M +Sp3cFbl1AK92beEgTIIPUuF4+kJyxVB5resNJM5NLwDpm4PxN4+4tMp/sJATZbsPx1p AgRox0d4Np09sTj3IapMSy6sZbc2gcmGL+ssruxemS0vOmzvoSk6iq1AIAhzmgi+N2Iq vJ1EBXIHW9XIh9oNKxnL2b2BQg9EfD7fYoFVRiMKUoWByZwLU1LDVg5qkhThqnr5/mci Dy5w== X-Gm-Message-State: ALoCoQlmEdc/qCrYgzy0IwDgLsyxGkMveBebEEbdFB13tgNgD8wIOq+JU0f/gc11i2eRlvWce2Jy X-Received: by 10.68.185.67 with SMTP id fa3mr7141640pbc.113.1445023369402; Fri, 16 Oct 2015 12:22:49 -0700 (PDT) Received: from ip-100-127-144-209.ec2.internal ([69.53.245.40]) by smtp.gmail.com with ESMTPSA id yt3sm2334873pbc.31.2015.10.16.12.22.47 (version=TLS1 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Fri, 16 Oct 2015 12:22:48 -0700 (PDT) Sender: Warner Losh Subject: Re: svn commit: r289405 - head/sys/ufs/ffs Mime-Version: 1.0 (Mac OS X Mail 8.2 \(2104\)) Content-Type: multipart/signed; boundary="Apple-Mail=_7FB987D8-D45D-47AC-8C10-CDCA9B1DCE46"; protocol="application/pgp-signature"; micalg=pgp-sha512 X-Pgp-Agent: GPGMail 2.5.2 From: Warner Losh In-Reply-To: <20151016131940.GE42243@zxy.spb.ru> Date: Fri, 16 Oct 2015 13:22:44 -0600 Cc: Warner Losh , src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Message-Id: <3ADA7934-3EE1-449E-A8D1-723B73020C13@bsdimp.com> References: <201510160306.t9G3622O049128@repo.freebsd.org> <20151016131940.GE42243@zxy.spb.ru> To: Slawa Olhovchenkov X-Mailer: Apple Mail (2.2104) X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 16 Oct 2015 19:22:55 -0000 --Apple-Mail=_7FB987D8-D45D-47AC-8C10-CDCA9B1DCE46 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 > On Oct 16, 2015, at 7:19 AM, Slawa Olhovchenkov = wrote: >=20 > On Fri, Oct 16, 2015 at 03:06:02AM +0000, Warner Losh wrote: >=20 >> Author: imp >> Date: Fri Oct 16 03:06:02 2015 >> New Revision: 289405 >> URL: https://svnweb.freebsd.org/changeset/base/289405 >>=20 >> Log: >> Do not relocate extents to make them contiguous if the underlying = drive can do >> deletions. Ability to do deletions is a strong indication that this >> optimization will not help performance. It will only generate extra = write >> traffic. These devices are typically flash based and have a limited = number of >> write cycles. In addition, making the file contiguous in LBA space = doesn't >> improve the access times from flash devices because they have no = seek time. >=20 > In reality, flash devices have seek time, about 0.1ms. > Many flash devices can do 8 simultaneously "seek" (I think NVMe can do > more). That=E2=80=99s just not true. tREAD for most flash is a few tens of = microseconds. The streaming time is at most 10 microseconds. There=E2=80=99s no =E2=80=9Csee= k=E2=80=9D time in the classic sense. Once you get the data, you have it. There=E2=80=99s no extra = =E2=80=9Cread time=E2=80=9D in the NAND flash parts. And the number of simultaneous reads depends a lot on how the flash = vendor organized the flash. Many of today=E2=80=99s designs use 8 or 16 die = parts that have 2 to 4 planes on them, giving a parallelism in the 16-64 range. And = that=E2=80=99s before we get into innovative strategies that use partial page reads to = decrease tREAD time and novel data striping methods. Seek time, as a separate operation, simply doesn=E2=80=99t exist. Furthermore, NAND-based devices are log-structured with garbage = collection for both retention and to deal with retired blocks in the underlying = NAND. The relationship between LBA ranges and where the data is at any given time = on the NAND is almost uncorrelated. So, rearranging data so that it is in LBA contiguous ranges doesn=E2=80=99= t help once you=E2=80=99re above the FFS block level. Warner --Apple-Mail=_7FB987D8-D45D-47AC-8C10-CDCA9B1DCE46 Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc Content-Description: Message signed with OpenPGP using GPGMail -----BEGIN PGP SIGNATURE----- Comment: GPGTools - https://gpgtools.org iQIcBAEBCgAGBQJWIU6EAAoJEGwc0Sh9sBEAbIYP/RtYW6TeKYHBOuL2JWV3Srud 6z6oXEp/U8dq1fZSrvJuKCxXaZXbFAaDSWabv1qayx+xhWDaJljorQIzlhVuSmOC Mvk5pZMEMHcEnxquZ9QT9rAfYXtUgbpBAhjeQsKwk5USb+5oTL1dzkYZZkS0CwhM /aB8PaKX3iMvRgsr540ZdfXOCpHA1K7ntLr5Eb9ZETZ6eexrhQUE/+wIVrUpr+kt gGPUNRjr375jAiObt6PWzl32OlnfJHTvU+R0N5ZVPWNMBGurLWiNGrT4BCMM4KLj Xc4Kaiv/AkcJjI8q2EdlprUDH7dyHTiXndYHgI7VEVzv3JHa7QIvMZLk5UVUCYCr Xs4BX0SdZ2xaNYi1JUPkoRxv6bsrpKMRtfH6WuJAKJwgGEfJhMkocFXtYhl/JUbO Oli7DXKEYd3KwRA9Acn/4/RWk7unL+j4rWQMiWtzTA5KHxh+9kTP0W6Y6pFsjKFv zl1sZLw5ACUipRJuCJLBdUn8IdrMR1h3AOJqmdx5VMPIaYTGF8nLqhtuykyTutTA Ta8z+g3DIxc7NO7gI6jJ//L7L2VsUMjvwLG8L+P3HvFVslhbPn9+XK3gixEWYiB2 aq/SW3dFWqvItmo0hD394ZRN/+sf/jpk026MrrC/e9+t6no+VvBxu1BZQIL5nnUh UMJYjYECkz5UT/CIzgq0 =bUtC -----END PGP SIGNATURE----- --Apple-Mail=_7FB987D8-D45D-47AC-8C10-CDCA9B1DCE46--