Date: Wed, 19 Dec 2012 18:24:23 +0000 From: "Poul-Henning Kamp" <phk@phk.freebsd.dk> To: Konstantin Belousov <kostikbel@gmail.com> Cc: mjacob@freebsd.org, freebsd-arch@freebsd.org Subject: Re: Unmapped I/O Message-ID: <17479.1355941463@critter.freebsd.dk> In-Reply-To: <20121219172320.GW71906@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>
next in thread | previous in thread | raw e-mail | index | archive | help
-------- In message <20121219172320.GW71906@kib.kiev.ua>, Konstantin Belousov writes: >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. 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. >Also, as I understand the history, VMIO buffers, or unified page/buffer >cache, only appeared in the FreeBSD. Correct, but truth to be told, they have probably delayed our implementation of unmapped buffers by about 10 years... 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. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?17479.1355941463>