[PATCH v2] sched/preempt: Tell about PREEMPT_DYNAMIC on kernel headers

[Frederic Weisbecker]

On Wed, Feb 02, 2022 at 06:24:09PM +0000, Valentin Schneider wrote:
> On 02/02/22 15:59, Frederic Weisbecker wrote:
> > Displaying "PREEMPT" on kernel headers when CONFIG_PREEMPT_DYNAMIC=y
> > can be misleading for anybody involved in remote debugging because it
> > is then not guaranteed that there is an actual preemption behaviour. It
> > depends on default Kconfig or boot defined choices.
> >
> > Therefore, tell about PREEMPT_DYNAMIC on static kernel headers and leave
> > the search for the actual preemption behaviour to browsing dmesg.
> >
> 
> Looks sensible. One small further cleanup nit below, otherwise:
> 
> Reviewed-by: Valentin Schneider <valentin.schneider@xxxxxxx>
[...]
> 
> I got suspicious of that PREEMPT_RT line, but it works because
> PREEMPT_BUILD and PREEMPT_RT are mutually exclusive. Nevertheless, could we
> clear out the ambiguity and make that into:
> 
> if   [ -n "$PREEMPT_RT" ] ;      then CONFIG_FLAGS="$CONFIG_FLAGS PREEMPT_RT";
> elif [ -n "$PREEMPT_DYNAMIC" ] ; then CONFIG_FLAGS="$CONFIG_FLAGS PREEMPT_DYNAMIC";
> elif [ -n "$PREEMPT" ] ;         then CONFIG_FLAGS="$CONFIG_FLAGS PREEMPT";
> fi

Good point!

Here you go:

---
From: Frederic Weisbecker <frederic@xxxxxxxxxx>
Date: Wed, 2 Feb 2022 15:59:54 +0100
Subject: [PATCH] sched/preempt: Tell about PREEMPT_DYNAMIC on kernel headers

Displaying "PREEMPT" on kernel headers when CONFIG_PREEMPT_DYNAMIC=y
can be misleading for anybody involved in remote debugging because it
is then not guaranteed that there is an actual preemption behaviour. It
depends on default Kconfig or boot defined choices.

Therefore, tell about PREEMPT_DYNAMIC on static kernel headers and leave
the search for the actual preemption behaviour to browsing dmesg.

Reviewed-by: Valentin Schneider <valentin.schneider@xxxxxxx>
Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
---
 init/Makefile       |  3 ++-
 scripts/mkcompile_h | 17 ++++++++++++-----
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/init/Makefile b/init/Makefile
index 06326e304384..d82623d7fc8e 100644
--- a/init/Makefile
+++ b/init/Makefile
@@ -31,7 +31,8 @@ quiet_cmd_compile.h = CHK     $@
       cmd_compile.h = \
 	$(CONFIG_SHELL) $(srctree)/scripts/mkcompile_h $@	\
 	"$(UTS_MACHINE)" "$(CONFIG_SMP)" "$(CONFIG_PREEMPT_BUILD)"	\
-	"$(CONFIG_PREEMPT_RT)" "$(CONFIG_CC_VERSION_TEXT)" "$(LD)"
+	"$(CONFIG_PREEMPT_DYNAMIC)" "$(CONFIG_PREEMPT_RT)" \
+	"$(CONFIG_CC_VERSION_TEXT)" "$(LD)"
 
 include/generated/compile.h: FORCE
 	$(call cmd,compile.h)
diff --git a/scripts/mkcompile_h b/scripts/mkcompile_h
index 6a2a04d92f42..ca40a5258c87 100755
--- a/scripts/mkcompile_h
+++ b/scripts/mkcompile_h
@@ -5,9 +5,10 @@ TARGET=$1
 ARCH=$2
 SMP=$3
 PREEMPT=$4
-PREEMPT_RT=$5
-CC_VERSION="$6"
-LD=$7
+PREEMPT_DYNAMIC=$5
+PREEMPT_RT=$6
+CC_VERSION="$7"
+LD=$8
 
 # Do not expand names
 set -f
@@ -41,8 +42,14 @@ fi
 UTS_VERSION="#$VERSION"
 CONFIG_FLAGS=""
 if [ -n "$SMP" ] ; then CONFIG_FLAGS="SMP"; fi
-if [ -n "$PREEMPT" ] ; then CONFIG_FLAGS="$CONFIG_FLAGS PREEMPT"; fi
-if [ -n "$PREEMPT_RT" ] ; then CONFIG_FLAGS="$CONFIG_FLAGS PREEMPT_RT"; fi
+
+if [ -n "$PREEMPT_RT" ] ; then
+	CONFIG_FLAGS="$CONFIG_FLAGS PREEMPT_RT"
+elif [ -n "$PREEMPT_DYNAMIC" ] ; then
+	CONFIG_FLAGS="$CONFIG_FLAGS PREEMPT_DYNAMIC"
+elif [ -n "$PREEMPT" ] ; then
+	CONFIG_FLAGS="$CONFIG_FLAGS PREEMPT"
+fi
 
 # Truncate to maximum length
 UTS_LEN=64
-- 
2.25.1