Kernel 2.6: new features and older computers

Greetings,

I am looking for some information on the issues listed below for two reasons. One is an article I am writing for a magazine, the other (as the coordinator of the non-profit RULE project, see my signature) is to understand if, how and how much the next linux kernel can be kept compatible with older computers.

Any feedback is welcome. Should you have the time and right mood to answer here or privately with detailed explanations, thanks a thousand in advance. If not, please just point me to the relevant stuff to read (be it URLs, email threads, comments in specific source files, whatever). I have already downloaded the "wonderful world of Linux 2.6" and the documents pointed in it.

On to the questions now:

1) minimal hw requirements (RAM, disk...) both to *use* and to *compile* the kernel

2) Which compilation switches could be used, if any, to lessen the above requirements and increase performance on obsolete systems (which in RULE means starting from 386/486/586 CPUs, 16+ MB RAM, hard disk ~ 400/500 MB, and the kind of peripherals used 6/7 years ago)

3) Details on how the build system is changed
4) What is RCU and which kind of performances it will improve
5) Online Kernel-related tutorials which I could/should mention in the "resource" section of the article
6) Anything else you might find relevant

Thanks again,

Marco Fioretti

Marco Fioretti                 m.fioretti, at the server inwind.it
Red Hat for low memory         http://www.rule-project.org/en/

Hello, Marco,

I can help with one of these...

RCU is a locking mechanism that is useful primarily for read-mostly data structures. It can be thought of as a reader-writer lock in which the readers need not actually do anything, which means that you can get substantial performance improvements in read-mostly situations. The writers must perform updates in a careful manner to avoid messing up the readers. In particular, if a writer removes an element from a list, it must wait for a "grace period" before freeing up the element, since readers might still be referencing it. RCU provides primitives that wait for grace periods to elapse.

The best introduction to RCU is probably:

	http://www.linuxjournal.com/article.php?sid=6993

More information on RCU, including performance comparisons in the Linux kernel may be found at:

http://www.rdrop.com/users/paulmck/rclock/

Thanx, Paul