linux-kernel - [PATCH RT 7/8] tracing: make preempt_lazy and migrate

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Message-Id: <0012457a5fe618e36a20b4d1b27265be51c6e8b1.1583783251.git.zanussi@kernel.org>
Date:   Mon,  9 Mar 2020 14:47:52 -0500
From:   zanussi@...nel.org
To:     LKML <linux-kernel@...r.kernel.org>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Carsten Emde <C.Emde@...dl.org>,
        John Kacur <jkacur@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Daniel Wagner <wagi@...om.org>,
        Tom Zanussi <zanussi@...nel.org>
Subject: [PATCH RT 7/8] tracing: make preempt_lazy and migrate_disable counter smaller

From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

v4.14.172-rt78-rc1 stable review patch.
If anyone has any objections, please let me know.

-----------


[ Upstream commit dd430bf5ecb40f9a89679c85868826475d71de54 ]

The migrate_disable counter should not exceed 255 so it is enough to
store it in an 8bit field.
With this change we can move the `preempt_lazy_count' member into the
gap so the whole struct shrinks by 4 bytes to 12 bytes in total.
Remove the `padding' field, it is not needed.
Update the tracing fields in trace_define_common_fields() (it was
missing the preempt_lazy_count field).

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Tom Zanussi <zanussi@...nel.org>
---
 include/linux/trace_events.h | 3 +--
 kernel/trace/trace_events.c  | 4 ++--
 2 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index edd1e42e8a2f7..01e9ab3107531 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -62,8 +62,7 @@ struct trace_entry {
 	unsigned char		flags;
 	unsigned char		preempt_count;
 	int			pid;
-	unsigned short		migrate_disable;
-	unsigned short		padding;
+	unsigned char		migrate_disable;
 	unsigned char		preempt_lazy_count;
 };
 
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 60e371451ec31..edd43841c94ad 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -187,8 +187,8 @@ static int trace_define_common_fields(void)
 	__common_field(unsigned char, flags);
 	__common_field(unsigned char, preempt_count);
 	__common_field(int, pid);
-	__common_field(unsigned short, migrate_disable);
-	__common_field(unsigned short, padding);
+	__common_field(unsigned char, migrate_disable);
+	__common_field(unsigned char, preempt_lazy_count);
 
 	return ret;
 }
-- 
2.14.1