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kdump-lib-initramfs: Fix performance regression in kdump_get_conf_val

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Resolves: https://issues.redhat.com/browse/RHEL-137945
Upstream: kdump-utils
Conflict: None

commit b43908c20f5a028c60b0096006a26a6e52a01279
Author: Philipp Rudo <prudo@redhat.com>
Date:   Wed Jan 14 15:54:25 2026 +0100

    kdump-lib-initramfs: Fix performance regression in kdump_get_conf_val

    Rewriting kdump_get_conf_val in Bash lead to a massive performance
    regression. On my test system starting the kdump service took

    $ time kdumpctl start
    real    0m13.134s
    user    0m8.828s
    sys     0m7.450s

    which is ~20 times slower compared to kdump-utils-1.0.59-1.fc44 with

    $ time kdumpctl start
    real    0m0.641s
    user    0m0.208s
    sys     0m0.538s

    Looking at the traces shows that this is caused because Bash now has to
    handle the whole kdump.conf, including the extensive comment at the
    start, every time kdump_get_conf_val is called. This is done multiple
    times when starting the kdump service and is often cloaked by other
    functions, e.g. is_ssh_dump_target() or get_save_path().

    To fix the issue remove comments and empty lines in a regex again so
    that the Bash code only has to handle valid config entries. With this
    change alone the performance is almost as good as the original version
    with

    $ time kdumpctl start
    real    0m0.780s
    user    0m0.330s
    sys     0m0.604s

    In the long run it would make sense to also reduce the number of calls
    to kdump_get_conf_val.

    This patch also fixes the issue that subsequent blanks are replaced by a
    single space. Usually this is not an issue but there are corner cases,
    e.g. in printf-like format strings passed as an argument, where the new
    behaviour is undesirable.

    Fixes: d81109c ("kdump-lib-initramfs: rewrite kdump_get_conf_val")
    Signed-off-by: Philipp Rudo <prudo@redhat.com>

Signed-off-by: Philipp Rudo <prudo@redhat.com>
This commit is contained in:
Philipp Rudo 2026-01-20 13:44:19 +01:00
parent 29785765ac
commit 24edf00fb8
2 changed files with 132 additions and 0 deletions
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131
0015-kdump-lib-initramfs-Fix-performance-regression-in-kd.patch Normal file
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@ -0,0 +1,131 @@
From b43908c20f5a028c60b0096006a26a6e52a01279 Mon Sep 17 00:00:00 2001
From: Philipp Rudo <prudo@redhat.com>
Date: Wed, 14 Jan 2026 15:54:25 +0100
Subject: [PATCH] kdump-lib-initramfs: Fix performance regression in
kdump_get_conf_val
Rewriting kdump_get_conf_val in Bash lead to a massive performance
regression. On my test system starting the kdump service took
$ time kdumpctl start
real 0m13.134s
user 0m8.828s
sys 0m7.450s
which is ~20 times slower compared to kdump-utils-1.0.59-1.fc44 with
$ time kdumpctl start
real 0m0.641s
user 0m0.208s
sys 0m0.538s
Looking at the traces shows that this is caused because Bash now has to
handle the whole kdump.conf, including the extensive comment at the
start, every time kdump_get_conf_val is called. This is done multiple
times when starting the kdump service and is often cloaked by other
functions, e.g. is_ssh_dump_target() or get_save_path().
To fix the issue remove comments and empty lines in a regex again so
that the Bash code only has to handle valid config entries. With this
change alone the performance is almost as good as the original version
with
$ time kdumpctl start
real 0m0.780s
user 0m0.330s
sys 0m0.604s
In the long run it would make sense to also reduce the number of calls
to kdump_get_conf_val.
This patch also fixes the issue that subsequent blanks are replaced by a
single space. Usually this is not an issue but there are corner cases,
e.g. in printf-like format strings passed as an argument, where the new
behaviour is undesirable.
Fixes: d81109c ("kdump-lib-initramfs: rewrite kdump_get_conf_val")
Signed-off-by: Philipp Rudo <prudo@redhat.com>
---
kdump-lib-initramfs.sh | 66 ++++++++++++++++++++++--------------------
1 file changed, 34 insertions(+), 32 deletions(-)
diff --git a/kdump-lib-initramfs.sh b/kdump-lib-initramfs.sh
index 6f5d6db..6c64106 100755
--- a/kdump-lib-initramfs.sh
+++ b/kdump-lib-initramfs.sh
@@ -30,38 +30,40 @@ kdump_get_conf_val()
_found=""
[ -f "$KDUMP_CONFIG_FILE" ] || return
- while read -r _line; do
- _line="$(echo "$_line" | tr -s "[:blank:]" " ")"
- case "$_line" in
- "" | \#*)
- continue
- ;;
- *\#*)
- _line="${_line%%\#*}"
- _line="${_line% }"
- ;;
- esac
-
- _opt=${_line%% *}
- _val=${_line#* }
-
- case "$_val" in
- \"*\")
- # Remove quotes
- _val="${_val#\"}"
- _val="${_val%\"}"
- ;;
- esac
-
- if [ -z "$_to_find" ]; then
- echo "$_opt $_val"
- elif echo "$_opt" | grep -q -E "^($_to_find)$"; then
- # make sure to only return the last match to mirror the
- # old behavior
- _found="$_val"
- fi
- done < "$KDUMP_CONFIG_FILE"
- [ -n "$_found" ] && echo "$_found"
+
+ # On lines that are _not_ comments or empty remove...
+ # Note: The additional braces {} are required as piping into a while
+ # loop creates a sub-shell. So without the braces $_found would only be
+ # set inside the loop but empty outside of it.
+ grep -Ev -e '^\s*#' -e '^\s*$' "$KDUMP_CONFIG_FILE" | {
+ while read -r _opt _val; do
+ # ...trailing comments...
+ case "$_val" in
+ *\#*)
+ _val="${_val%%#*}"
+ _val="${_val%"${_val##*[![:space:]]}"}"
+ ;;
+ esac
+
+ # ...quotes
+ case "$_val" in
+ \"*\")
+ _val="${_val#\"}"
+ _val="${_val%\"}"
+ ;;
+ esac
+
+ if [ -z "$_to_find" ]; then
+ echo "$_opt $_val"
+ elif echo "$_opt" | grep -q -E "^($_to_find)$"; then
+ # make sure to only return the last match to
+ # mirror the old behavior
+ _found="$_val"
+ fi
+ done
+
+ [ -n "$_found" ] && echo "$_found"
+ }
# make sure we return 0 even when a option isn't set
return 0
--
2.52.0

1
kdump-utils.spec
View File

@ -22,6 +22,7 @@ Patch11: 0011-kdump.sh-Skip-num-threads-when-E-and-F-option-is-pre.patch
Patch12: 0012-powerpc-consider-CPU-count-while-calculating-crashke.patch
Patch13: 0013-powerpc-Set-nr_cpus-16-for-kdump-kernel.patch
Patch14: 0014-kexec-kdump-howto.txt-update-paragraphs-related-to-d.patch
Patch15: 0015-kdump-lib-initramfs-Fix-performance-regression-in-kd.patch
%ifarch ppc64 ppc64le