linux-kernel - [tip: timers/core] timers: Optimize get_timer_[this_]cpu

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Message-ID: <173701493781.31546.11275183632173844475.tip-bot2@tip-bot2>
Date: Thu, 16 Jan 2025 08:08:57 -0000
From: "tip-bot2 for Zhongqiu Han" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Zhongqiu Han <quic_zhonhan@...cinc.com>,
 Thomas Gleixner <tglx@...utronix.de>,
 Frederic Weisbecker <frederic@...nel.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: timers/core] timers: Optimize get_timer_[this_]cpu_base()

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

Commit-ID:     3ec955713d9617059d2fc8f2816d0b95ace72256
Gitweb:        https://git.kernel.org/tip/3ec955713d9617059d2fc8f2816d0b95ace72256
Author:        Zhongqiu Han <quic_zhonhan@...cinc.com>
AuthorDate:    Tue, 31 Dec 2024 23:01:15 +08:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Thu, 16 Jan 2025 09:04:23 +01:00

timers: Optimize get_timer_[this_]cpu_base()

If a timer is deferrable and NO_HZ_COMMON is enabled, get_timer_cpu_base()
and get_timer_this_cpu_base() invoke per_cpu_ptr() and this_cpu_ptr()
twice.

While this seems to be cheap, get_timer_cpu_base() can be called in a loop
in lock_timer_base().

Optimize the functions by updating the base index for deferrable timers and
retrieving the actual base pointer once.

In both cases the resulting assembly code of those helpers becomes smaller,
which results in a ~30% execution time reduction for a lock_timer_base()
micro bench mark.

Signed-off-by: Zhongqiu Han <quic_zhonhan@...cinc.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Frederic Weisbecker <frederic@...nel.org>
Link: https://lore.kernel.org/all/20241231150115.1978342-1-quic_zhonhan@quicinc.com

---
 kernel/time/timer.c | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index a5860bf..40706cb 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -956,33 +956,29 @@ static int detach_if_pending(struct timer_list *timer, struct timer_base *base,
 static inline struct timer_base *get_timer_cpu_base(u32 tflags, u32 cpu)
 {
 	int index = tflags & TIMER_PINNED ? BASE_LOCAL : BASE_GLOBAL;
-	struct timer_base *base;
-
-	base = per_cpu_ptr(&timer_bases[index], cpu);
 
 	/*
 	 * If the timer is deferrable and NO_HZ_COMMON is set then we need
 	 * to use the deferrable base.
 	 */
 	if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && (tflags & TIMER_DEFERRABLE))
-		base = per_cpu_ptr(&timer_bases[BASE_DEF], cpu);
-	return base;
+		index = BASE_DEF;
+
+	return per_cpu_ptr(&timer_bases[index], cpu);
 }
 
 static inline struct timer_base *get_timer_this_cpu_base(u32 tflags)
 {
 	int index = tflags & TIMER_PINNED ? BASE_LOCAL : BASE_GLOBAL;
-	struct timer_base *base;
-
-	base = this_cpu_ptr(&timer_bases[index]);
 
 	/*
 	 * If the timer is deferrable and NO_HZ_COMMON is set then we need
 	 * to use the deferrable base.
 	 */
 	if (IS_ENABLED(CONFIG_NO_HZ_COMMON) && (tflags & TIMER_DEFERRABLE))
-		base = this_cpu_ptr(&timer_bases[BASE_DEF]);
-	return base;
+		index = BASE_DEF;
+
+	return this_cpu_ptr(&timer_bases[index]);
 }
 
 static inline struct timer_base *get_timer_base(u32 tflags)