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Sync DIAGNOSTIC performance comments with historical reality.

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Somehow, options(4) ended up with a bizarre claim that DIAGNOSTIC can
reduce performance by 15%.  While that might have been true at some
isolated point due to a bug, it's an outlier.  Since at least 2BSD,
DIAGNOSTIC has added asserts, resulting in at most
difficult-to-perceived performance degredation, and many people have
been running production systems (meaning systems they intend to use,
rather than debugging targets) with this option.    (The decision a
while ago to enable DIAGNOSTIC in -current's GENERIC reflects this; if
it really were a 15% hit such enabling by default would be unreasonable.)
This commit is contained in:
gdt 2014-07-23 20:13:13 +00:00
parent 582402eab5
commit c6a967921a
1 changed files with 9 additions and 2 deletions
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11
share/man/man4/options.4
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@ -1,4 +1,4 @@
.\" $NetBSD: options.4,v 1.437 2014/03/23 00:50:20 dholland Exp $
.\" $NetBSD: options.4,v 1.438 2014/07/23 20:13:13 gdt Exp $
.\"
.\" Copyright (c) 1996
.\" Perry E. Metzger. All rights reserved.
@ -604,11 +604,18 @@ Note that many parts of the kernel (typically device drivers) include their own
conditionals instead.
This option also turns on certain other options,
which may decrease system performance.
Systems with this option are not suitable for regular use, and are
intended only for debugging or looking for bugs.
.It Cd options DIAGNOSTIC
Adds code to the kernel that does internal consistency checks.
This code will cause the kernel to panic if corruption of internal data
structures is detected.
These checks can decrease performance up to 15%.
Historically, the performance degredation is sufficiently small that
it is reasonable for systems with
.Em options DIAGNOSTIC
to be in production use, with the real consideration not being
performance but instead a preference for more panics versus continued
operation with undetected problems.
.It Cd options LOCKDEBUG
Adds code to the kernel to detect incorrect use of locking primitives
(mutex, rwlock).