[TUHS] UNIX on S/370

Larry McVoy lm at mcvoy.com
Tue Nov 21 13:51:12 AEST 2017


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 at minnie.tuhs.org] On Behalf Of Noel Chiappa
> Sent: Monday, November 20, 2017 9:57 PM
> To: tuhs at tuhs.org
> Cc: jnc at mercury.lcs.mit.edu
> Subject: Re: [TUHS] UNIX on S/370
> 
>     > 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

-- 
---
Larry McVoy            	     lm at mcvoy.com             http://www.mcvoy.com/lm 


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