21 Nov
2017
21 Nov
'17
4:51 a.m.
Actually, how common was that? I know at SGI we did that with O_DIRECT
on files (and just automatically on the way for in networking and page
flipped on the way out). But it was a pile of work, you had to lock
all the pages so that the pageout daemon didn't page them out, etc.
So under what circumstances would Unix do DMA to/from user buffers
rather than bcopy it?
On Mon, Nov 20, 2017 at 10:15:58PM -0500, Ron Natalie wrote:
That's a common optimization, but the only real
requirement in the UNIX
kernel is the raw I/O bypasses the kernel buffer cache.
-----Original Message-----
From: TUHS [mailto:tuhs-bounces@minnie.tuhs.org] On Behalf Of Noel Chiappa
Sent: Monday, November 20, 2017 9:57 PM
To: tuhs(a)tuhs.org
Cc: jnc(a)mercury.lcs.mit.edu
Subject: Re: [TUHS] UNIX on S/370
--
---
Larry McVoy lm at mcvoy.com http://www.mcvoy.com/lm
From: Larry McVoy
So tape I can see being more weird, but
isn't raw disk just "don't put
it in buffer cache"?
One machines/controllers which are capable of it, with raw devices DMA
happens directly into the buffers in the process (which obviously has to be
resident while the I/O is happening).
Noel