[src/trunk]: src/sys/sys Comment on CTASSERT() in COND_SET_STRUCT(); this is ...

[rin <rin%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/2efda10d07c9
branches:  trunk
changeset: 953598:2efda10d07c9
user:      rin <rin%NetBSD.org@localhost>
date:      Sun Mar 14 02:53:57 2021 +0000

description:
Comment on CTASSERT() in COND_SET_STRUCT(); this is a sanity check to
avoid hashing/assigning large structure. Upper-bound is arbitrary, but
be carefully for performance penalty if bumping.

Thanks christos for discussion.

diffstat:

 sys/sys/systm.h |  7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)

diffs (21 lines):

diff -r 76fe8c67902b -r 2efda10d07c9 sys/sys/systm.h
--- a/sys/sys/systm.h   Sun Mar 14 01:44:37 2021 +0000
+++ b/sys/sys/systm.h   Sun Mar 14 02:53:57 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: systm.h,v 1.299 2021/03/10 13:27:51 simonb Exp $       */
+/*     $NetBSD: systm.h,v 1.300 2021/03/14 02:53:57 rin Exp $  */
 
 /*-
  * Copyright (c) 1982, 1988, 1991, 1993
@@ -192,6 +192,11 @@
 #ifdef _KERNEL
 #define COND_SET_STRUCT(dst, src, allow) \
        do { \
+               /* \
+                * Make sure we don't end up hashing/assigning large \
+                * structure for performance. Upper-bound is arbitrary, \
+                * but consider before bumping. \
+                */ \
                CTASSERT(sizeof(src) < 32); \
                if (allow) \
                        dst = src; \