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SubjectRe: [RFC] - Some notions that I would like comments on
On Mon, 19 Jul 1999, Stephen C. Tweedie wrote:
> > right - i should have specified that the "readbehind" has negative effects
> > for random accesses, but are not much of an issue for sequential accesses
> > of an mmap'd file.
>
> No. "Readaround" works well for the random access patterns seen when
> accessing executable code. When running a library function, you
> often end up invoking a lot of related functions which are called by
> that function, and those are as likely to be earlier in the library
> image as later.

i understand why a little readbehind can be effective in the random case,
and even have some experimental evidence that this is true. have you
measured this or do you have a study on it? i'm not convinced that
significant amounts of readbehind are effective -- diminishing returns and
all that. that's why i think quarter-cluster alignment is much better
than cluster-alignment.

plus, libraries aren't the only thing that are mapped. what would the
best readaround strategy be for a mapped randomly accessed sleepycat index
file, for instance?

> A decent performance study of the effects of these changes would be far
> more interesting than a simple list of the possible code variations!

yes, i've considered that. but i'd like some discussion about what you
and everyone else here thinks would be interesting to try. i know what
i'd like to try, but i'm a new kid.

- Chuck Lever
--
corporate: <chuckl@netscape.com>
personal: <chucklever@netscape.net> or <cel@monkey.org>

The Linux Scalability project:
http://www.citi.umich.edu/projects/linux-scalability/


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