Date: Wed, 19 Dec 2012 20:36:00 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: Poul-Henning Kamp <phk@phk.freebsd.dk> Cc: mjacob@freebsd.org, freebsd-arch@freebsd.org Subject: Re: Unmapped I/O Message-ID: <20121219183600.GX71906@kib.kiev.ua> In-Reply-To: <17479.1355941463@critter.freebsd.dk> 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>
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--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--
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