linux-kernel - [tip: perf/core] perf: Shrink the size of the recursion counter.

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Message-ID: <172052531830.2215.8399866231682397481.tip-bot2@tip-bot2>
Date: Tue, 09 Jul 2024 11:41:58 -0000
From: "tip-bot2 for Sebastian Andrzej Siewior" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 Marco Elver <elver@...gle.com>, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: perf/core] perf: Shrink the size of the recursion counter.

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     5af42f928f3ac555c228740fb4a92d05b19fdd49
Gitweb:        https://git.kernel.org/tip/5af42f928f3ac555c228740fb4a92d05b19fdd49
Author:        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
AuthorDate:    Thu, 04 Jul 2024 19:03:38 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 09 Jul 2024 13:26:35 +02:00

perf: Shrink the size of the recursion counter.

There are four recursion counter, one for each context. The type of the
counter is `int' but the counter is used as `bool' since it is only
incremented if zero.
The main goal here is to shrink the whole struct into 32bit int which
can later be added task_struct into an existing hole.

Reduce the type of the recursion counter to an unsigned char, keep the
increment/ decrement operation.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: Marco Elver <elver@...gle.com>
Link: https://lore.kernel.org/r/20240704170424.1466941-5-bigeasy@linutronix.de
---
 kernel/events/callchain.c | 2 +-
 kernel/events/core.c      | 2 +-
 kernel/events/internal.h  | 4 ++--
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c
index 1273be8..ad57944 100644
--- a/kernel/events/callchain.c
+++ b/kernel/events/callchain.c
@@ -29,7 +29,7 @@ static inline size_t perf_callchain_entry__sizeof(void)
 				 sysctl_perf_event_max_contexts_per_stack));
 }
 
-static DEFINE_PER_CPU(int, callchain_recursion[PERF_NR_CONTEXTS]);
+static DEFINE_PER_CPU(u8, callchain_recursion[PERF_NR_CONTEXTS]);
 static atomic_t nr_callchain_events;
 static DEFINE_MUTEX(callchain_mutex);
 static struct callchain_cpus_entries *callchain_cpus_entries;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 73e1b02..53e2750 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9765,7 +9765,7 @@ struct swevent_htable {
 	int				hlist_refcount;
 
 	/* Recursion avoidance in each contexts */
-	int				recursion[PERF_NR_CONTEXTS];
+	u8				recursion[PERF_NR_CONTEXTS];
 };
 
 static DEFINE_PER_CPU(struct swevent_htable, swevent_htable);
diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index 386d21c..7f06b79 100644
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -208,7 +208,7 @@ arch_perf_out_copy_user(void *dst, const void *src, unsigned long n)
 
 DEFINE_OUTPUT_COPY(__output_copy_user, arch_perf_out_copy_user)
 
-static inline int get_recursion_context(int *recursion)
+static inline int get_recursion_context(u8 *recursion)
 {
 	unsigned char rctx = interrupt_context_level();
 
@@ -221,7 +221,7 @@ static inline int get_recursion_context(int *recursion)
 	return rctx;
 }
 
-static inline void put_recursion_context(int *recursion, int rctx)
+static inline void put_recursion_context(u8 *recursion, int rctx)
 {
 	barrier();
 	recursion[rctx]--;