From owner-freebsd-arch@FreeBSD.ORG Wed Dec 19 18:36:05 2012 Return-Path: Delivered-To: freebsd-arch@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 02728925; Wed, 19 Dec 2012 18:36:04 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) by mx1.freebsd.org (Postfix) with ESMTP id 902808FC0A; Wed, 19 Dec 2012 18:36:04 +0000 (UTC) Received: from tom.home (kostik@localhost [127.0.0.1]) by kib.kiev.ua (8.14.5/8.14.5) with ESMTP id qBJIa026055191; Wed, 19 Dec 2012 20:36:00 +0200 (EET) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.7.3 kib.kiev.ua qBJIa026055191 Received: (from kostik@localhost) by tom.home (8.14.5/8.14.5/Submit) id qBJIa0aF055190; Wed, 19 Dec 2012 20:36:00 +0200 (EET) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Wed, 19 Dec 2012 20:36:00 +0200 From: Konstantin Belousov To: Poul-Henning Kamp Subject: Re: Unmapped I/O Message-ID: <20121219183600.GX71906@kib.kiev.ua> References: <20121219135451.GU71906@kib.kiev.ua> <50D1D2BD.80107@freebsd.org> <50D1ECC5.2070209@freebsd.org> <17252.1355935960@critter.freebsd.dk> <20121219172320.GW71906@kib.kiev.ua> <17479.1355941463@critter.freebsd.dk> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="Ge5ZftkQPdHHxjIb" Content-Disposition: inline In-Reply-To: <17479.1355941463@critter.freebsd.dk> User-Agent: Mutt/1.5.21 (2010-09-15) X-Spam-Status: No, score=-2.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FREEMAIL_FROM,NML_ADSP_CUSTOM_MED autolearn=no version=3.3.2 X-Spam-Checker-Version: SpamAssassin 3.3.2 (2011-06-06) on tom.home Cc: mjacob@freebsd.org, freebsd-arch@freebsd.org X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 19 Dec 2012 18:36:05 -0000 --Ge5ZftkQPdHHxjIb Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Dec 19, 2012 at 06:24:23PM +0000, Poul-Henning Kamp wrote: > -------- > In message <20121219172320.GW71906@kib.kiev.ua>, Konstantin Belousov writ= es: >=20 > >Still, the i386 cannot have much benefit from the unmapped buffers, > >just because thre is no facilities similar to the direct map for amd64. > >i386 must use transient mapping even for unmapped buffers to copy > >the data to the usermode. >=20 > Wrong, a Adaptec 1542 could DMA directly into or out of any spot > of memory and that could have been mapped in userland but not in > kernel. And how this can be used while keeping on-disk data coherent with the buffer ? It can by used by physio, but not for the normal file i/o, which caches the file data in the vnode pages or buffers for non-unified cache. The transient mapping is needed to copy between kernel buffer and usermode address on i386. >=20 > >Also, as I understand the history, VMIO buffers, or unified page/buffer > >cache, only appeared in the FreeBSD. >=20 > Correct, but truth to be told, they have probably delayed our > implementation of unmapped buffers by about 10 years... Mapped bufers only become an issue on really multi-core machines. Before large SMP become ubiquitous, additional complexity of the transient mappings definitely not worth it. >=20 > I don't blame John & David however, making that full leap in > one go would have required the mythical HeldenProgrammer, there > were a lot of cruft we had to get out of the way first. >=20 > --=20 > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > phk@FreeBSD.ORG | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe =20 > Never attribute to malice what can adequately be explained by incompetenc= e. --Ge5ZftkQPdHHxjIb Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.19 (FreeBSD) iQIcBAEBAgAGBQJQ0gkPAAoJEJDCuSvBvK1B98cP/RVpqg6fWzCmvT2do78GRYhX +zDWRQyfYppKmer9ymth2xuFBpa+OVNhhRqnSQ2iV9SBEIG834lFK18t1hUOkP++ 8Lg1YZMWRQ8WW5eRaLeA3T7pf07YhuTZchMgwxG9zi5lGXBOOHIrDcEQ92qQq8fY ImMPj8cBusWL+Z09s85KFAjGvdsC8pVZXRVxXhaRfC59pLEowdxMIF5GQKUzbYqz FYpwd2NFCMN5ZMCAJHudxg7dwqfEFAIKLYpouEzzNXS4VOdgher4+WS7sdYsMeMn Htn15r/qc/TikItxzwrEA8LZbw6w/ASLau61dMc0alfc2RbPcLfTdbtQ62v83nIp TsglyGnuaSbs7+h8B5kz/hHZKe9Y8T6lF9KJC/YkmvuVh5mLnK/vmSZromUkpDKR cPaY2cZ7z8E2g8kRND2JLjUjXh083BiDdB+0F0eYdW+QbDJnJQYGRgwXaUegnDBA ZqAwVlg22px/tizYKpw5r2KBpXmFqd3GngH/KKQVkAxS6HItWBfzkTXjK2ReKGVq Sb9IihLcENNETgBO2xWMCd0ohAj9jYUpyMrtxSjqhDutw6ubk2kBH5rY89cQKgD7 Ks/fhn2Bd1VxkOQB4X1+LOpQzDPvDMPNDXzDKKdx6LSQN2aXec8wASogOrxnkjEZ bbQSqukY0Hp8PJYyaDjv =PCNw -----END PGP SIGNATURE----- --Ge5ZftkQPdHHxjIb--