This is a note to let you know that I've just added the patch titled
lib/Kconfig.debug: do not enable DEBUG_PREEMPT by default
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
lib-kconfig.debug-do-not-enable-debug_preempt-by-default.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From cc6003916ed46d7a67d91ee32de0f9138047d55f Mon Sep 17 00:00:00 2001
From: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
Date: Sat, 21 Jan 2023 12:39:42 +0900
Subject: lib/Kconfig.debug: do not enable DEBUG_PREEMPT by default
From: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
commit cc6003916ed46d7a67d91ee32de0f9138047d55f upstream.
In workloads where this_cpu operations are frequently performed,
enabling DEBUG_PREEMPT may result in significant increase in
runtime overhead due to frequent invocation of
__this_cpu_preempt_check() function.
This can be demonstrated through benchmarks such as hackbench where this
configuration results in a 10% reduction in performance, primarily due to
the added overhead within memcg charging path.
Therefore, do not to enable DEBUG_PREEMPT by default and make users aware
of its potential impact on performance in some workloads.
hackbench-process-sockets
debug_preempt no_debug_preempt
Amean 1 0.4743 ( 0.00%) 0.4295 * 9.45%*
Amean 4 1.4191 ( 0.00%) 1.2650 * 10.86%*
Amean 7 2.2677 ( 0.00%) 2.0094 * 11.39%*
Amean 12 3.6821 ( 0.00%) 3.2115 * 12.78%*
Amean 21 6.6752 ( 0.00%) 5.7956 * 13.18%*
Amean 30 9.6646 ( 0.00%) 8.5197 * 11.85%*
Amean 48 15.3363 ( 0.00%) 13.5559 * 11.61%*
Amean 79 24.8603 ( 0.00%) 22.0597 * 11.27%*
Amean 96 30.1240 ( 0.00%) 26.8073 * 11.01%*
Link: https://lkml.kernel.org/r/20230121033942.350387-1-42.hyeyoo@xxxxxxxxx
Signed-off-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
Acked-by: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Acked-by: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Ben Segall <bsegall@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Dennis Zhou <dennis@xxxxxxxxxx>
Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
Cc: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Luiz Capitulino <luizcap@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
lib/Kconfig.debug | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1136,13 +1136,16 @@ config DEBUG_TIMEKEEPING
config DEBUG_PREEMPT
bool "Debug preemptible kernel"
depends on DEBUG_KERNEL && PREEMPTION && TRACE_IRQFLAGS_SUPPORT
- default y
help
If you say Y here then the kernel will use a debug variant of the
commonly used smp_processor_id() function and will print warnings
if kernel code uses it in a preemption-unsafe way. Also, the kernel
will detect preemption count underflows.
+ This option has potential to introduce high runtime overhead,
+ depending on workload as it triggers debugging routines for each
+ this_cpu operation. It should only be used for debugging purposes.
+
menu "Lock Debugging (spinlocks, mutexes, etc...)"
config LOCK_DEBUGGING_SUPPORT
Patches currently in stable-queue which might be from 42.hyeyoo@xxxxxxxxx are
queue-5.10/lib-kconfig.debug-do-not-enable-debug_preempt-by-default.patch
