Date: Wed, 4 Jul 2001 21:12:33 -0600 From: "Kenneth D. Merry" <ken@kdm.org> To: Kevin Hui <khui@cs.toronto.edu> Cc: freebsd-questions@FreeBSD.ORG, freebsd-hackers@FreeBSD.ORG Subject: Re: Raw disk access in userland Message-ID: <20010704211233.A48146@panzer.kdm.org> In-Reply-To: <Pine.GSO.4.21.0107042015130.5050-100000@gardiner.cs>; from khui@cs.toronto.edu on Wed, Jul 04, 2001 at 08:18:51PM -0400 References: <20010704170844.A47113@panzer.kdm.org> <Pine.GSO.4.21.0107042015130.5050-100000@gardiner.cs>
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On Wed, Jul 04, 2001 at 20:18:51 -0400, Kevin Hui wrote: > Then the question is whether the kernel is copying data between userspace > and kernelspace or whether it just DMAs the data straight in/out of the > user program's address space. In Linux raw-io, given that it is a block > device and you are doing page-aligned block I/Os on it, is smart and does > zero copies. While it may seem to be jumping through hoops, maybe it does > have a performance advantage? The kernel copies between userland and the kernel. Ken -- Kenneth Merry ken@kdm.org To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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