linux-kernel - [RFC 1/3] softirq: Use preempt_latency

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Date:   Tue, 28 May 2019 17:16:22 +0200
From:   Daniel Bristot de Oliveira <bristot@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     williams@...hat.com, daniel@...stot.me,
        "Steven Rostedt (VMware)" <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Yangtao Li <tiny.windzz@...il.com>,
        Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>
Subject: [RFC 1/3] softirq: Use preempt_latency_stop/start to trace preemption

prempt_disable/enable tracepoints occurs only in the preemption
enabled <-> disable transition. As preempt_latency_stop() and
preempt_latency_start() already do this control, avoid code
duplication by using these functions in the softirq code as well.

RFC: Should we move preempt_latency_start/preempt_latency_stop
to a trace source file... or even a header?

Signed-off-by: Daniel Bristot de Oliveira <bristot@...hat.com>
Cc: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc: Matthias Kaehlcke <mka@...omium.org>
Cc: "Joel Fernandes (Google)" <joel@...lfernandes.org>
Cc: Frederic Weisbecker <frederic@...nel.org>
Cc: Yangtao Li <tiny.windzz@...il.com>
Cc: Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>
Cc: linux-kernel@...r.kernel.org
---
 kernel/sched/core.c |  4 ++--
 kernel/softirq.c    | 13 +++++--------
 2 files changed, 7 insertions(+), 10 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 874c427742a9..8c0b414e45dc 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3152,7 +3152,7 @@ static inline void sched_tick_stop(int cpu) { }
  * If the value passed in is equal to the current preempt count
  * then we just disabled preemption. Start timing the latency.
  */
-static inline void preempt_latency_start(int val)
+void preempt_latency_start(int val)
 {
 	if (preempt_count() == val) {
 		unsigned long ip = get_lock_parent_ip();
@@ -3189,7 +3189,7 @@ NOKPROBE_SYMBOL(preempt_count_add);
  * If the value passed in equals to the current preempt count
  * then we just enabled preemption. Stop timing the latency.
  */
-static inline void preempt_latency_stop(int val)
+void preempt_latency_stop(int val)
 {
 	if (preempt_count() == val)
 		trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 2c3382378d94..c9ad89c3dfed 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -108,6 +108,8 @@ static bool ksoftirqd_running(unsigned long pending)
  * where hardirqs are disabled legitimately:
  */
 #ifdef CONFIG_TRACE_IRQFLAGS
+extern void preempt_latency_start(int val);
+extern void preempt_latency_stop(int val);
 void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
 {
 	unsigned long flags;
@@ -130,12 +132,8 @@ void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
 		trace_softirqs_off(ip);
 	raw_local_irq_restore(flags);
 
-	if (preempt_count() == cnt) {
-#ifdef CONFIG_DEBUG_PREEMPT
-		current->preempt_disable_ip = get_lock_parent_ip();
-#endif
-		trace_preempt_off(CALLER_ADDR0, get_lock_parent_ip());
-	}
+	preempt_latency_start(cnt);
+
 }
 EXPORT_SYMBOL(__local_bh_disable_ip);
 #endif /* CONFIG_TRACE_IRQFLAGS */
@@ -144,8 +142,7 @@ static void __local_bh_enable(unsigned int cnt)
 {
 	lockdep_assert_irqs_disabled();
 
-	if (preempt_count() == cnt)
-		trace_preempt_on(CALLER_ADDR0, get_lock_parent_ip());
+	preempt_latency_stop(cnt);
 
 	if (softirq_count() == (cnt & SOFTIRQ_MASK))
 		trace_softirqs_on(_RET_IP_);
-- 
2.20.1