Messages in this thread | | | Date | Mon, 19 Jul 1999 11:08:32 -0400 (EDT) | From | Chuck Lever <> | Subject | Re: [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/
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.rutgers.edu Please read the FAQ at http://www.tux.org/lkml/
| |