From: satishc@microsoft.com (Satish Chittamuru) Subject: Re: Why are hard disk reads so much slower than writes? Date: 3 Dec 1992 19:41:15 GMT
In article <ByJysC.ILM@news.cso.uiuc.edu> jy10033@ehsn11.cen.uiuc.edu (Joshua M Yelon) writes:
> Juan writes:
>
> I would imagine that if iozone were performing lots of "read(fd, buf, 8192)"
> calls, then it would effectively cause this behavior:
>
> * iozone calls read(fd, buf, 8192)
> * kernel context-switches in.
> * kernel fetches a disk page (8192) bytes from disk into cache.
> * kernel copies 8192 bytes from cache into user buffer.
Does the kernel really copy the 8K bytes to user buffer? Can't it
map the cache to be the buffer block or if the user specifies a
buffer, then map the buffer to be part of the cache and then do a
copy-on-write etc? Does this require a very complicated cache/buffer
management?
> * iozone context switches back in.
-- Satish K. Chittamuru satishc@microsoft.com ===== Disclaimer: The opinions expressed herein, either stated or implied, are solely my own and do not reflect Microsoft's views in any manner.