Bug 219457 - CONFIG_NR_CPUS is insanely high for fedora
Summary: CONFIG_NR_CPUS is insanely high for fedora
Alias: None
Product: Fedora
Classification: Fedora
Component: kernel
Version: 6
Hardware: All
OS: Linux
Target Milestone: ---
Assignee: Dave Jones
QA Contact: Brian Brock
Depends On:
TreeView+ depends on / blocked
Reported: 2006-12-13 10:01 UTC by Arjan van de Ven
Modified: 2015-01-04 22:29 UTC (History)
2 users (show)

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Clone Of:
Last Closed: 2006-12-19 03:40:03 UTC
Type: ---

Attachments (Terms of Use)

Description Arjan van de Ven 2006-12-13 10:01:21 UTC
Description of problem:

The Fedora kernel has CONFIG_NR_CPUS set to 255, which is insanely high.
First of all, no systems exist that can have that many processors or cores (you
run out of apics well before that).
Second, even if they would exist they'd probably not run fedora. (and would cost
a milion bucks or more:0

The downsides are a massive waste of memory; for example just the irq_desc array
alone (in 2.6.19) is more than 2 megabytes just because of this, and a lot of
other things in memory scale likewise with CONFIG_NR_CPUS.

I would suggest a value of no larger than 64 (that also means that cpu bitmasks
fit in a long) for this value ... it wastes a lot less memory and generates a
lot better code in all the cpu mask operations..

Comment 1 Dave Jones 2006-12-19 03:40:03 UTC
fixed in update.

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