linux-kernel - [PATCH 22/32] softirq: Check enabled vectors before processing

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Date:   Tue, 12 Feb 2019 18:14:13 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Mauro Carvalho Chehab <mchehab@...pensource.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "David S . Miller" <davem@...emloft.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Pavan Kondeti <pkondeti@...eaurora.org>,
        Ingo Molnar <mingo@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: [PATCH 22/32] softirq: Check enabled vectors before processing

There is no need to process softirqs if none of those pending are
enabled. Check about that early to avoid unnecessary overhead.

Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Cc: Mauro Carvalho Chehab <mchehab@...pensource.com>
Cc: Joel Fernandes <joel@...lfernandes.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Pavan Kondeti <pkondeti@...eaurora.org>
Cc: Paul E . McKenney <paulmck@...ux.vnet.ibm.com>
Cc: David S . Miller <davem@...emloft.net>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
---
 include/linux/interrupt.h |  5 +++++
 kernel/softirq.c          | 21 +++++++++++----------
 2 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 346fb1e8e55b..161babfc1a0d 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -508,6 +508,11 @@ static inline void softirq_pending_set_mask(unsigned int pending)
 {
 	__this_cpu_or(local_softirq_data_ref, pending);
 }
+
+static inline int softirq_pending_enabled(void)
+{
+	return local_softirq_pending() & local_softirq_enabled();
+}
 #endif /* local_softirq_pending */
 
 /* map softirq index to softirq name. update 'softirq_to_name' in
diff --git a/kernel/softirq.c b/kernel/softirq.c
index d305b4c8d1a7..a2257a5aaa0b 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -181,7 +181,7 @@ void __local_bh_enable_ip(unsigned long ip, unsigned int cnt)
 	 */
 	preempt_count_sub(cnt - 1);
 
-	if (unlikely(!in_interrupt() && local_softirq_pending())) {
+	if (unlikely(!in_interrupt() && softirq_pending_enabled())) {
 		/*
 		 * Run softirq if any pending. And do it in its own stack
 		 * as we may be calling this deep in a task call stack already.
@@ -250,7 +250,7 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
 	int max_restart = MAX_SOFTIRQ_RESTART;
 	struct softirq_action *h;
 	bool in_hardirq;
-	__u32 pending;
+	__u32 pending, enabled;
 	int softirq_bit;
 
 	/*
@@ -260,7 +260,8 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
 	 */
 	current->flags &= ~PF_MEMALLOC;
 
-	pending = local_softirq_pending();
+	enabled = local_softirq_enabled();
+	pending = local_softirq_pending() & enabled;
 	account_irq_enter_time(current);
 
 	__local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET);
@@ -268,7 +269,7 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
 
 restart:
 	/* Reset the pending bitmask before enabling irqs */
-	softirq_pending_clear_mask(SOFTIRQ_ALL_MASK);
+	softirq_pending_clear_mask(pending);
 
 	local_irq_enable();
 
@@ -305,7 +306,7 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
 		rcu_softirq_qs();
 	local_irq_disable();
 
-	pending = local_softirq_pending();
+	pending = local_softirq_pending() & enabled;
 	if (pending) {
 		if (time_before(jiffies, end) && !need_resched() &&
 		    --max_restart)
@@ -331,7 +332,7 @@ asmlinkage __visible void do_softirq(void)
 
 	local_irq_save(flags);
 
-	pending = local_softirq_pending();
+	pending = softirq_pending_enabled();
 
 	if (pending && !ksoftirqd_running(pending))
 		do_softirq_own_stack();
@@ -360,7 +361,7 @@ void irq_enter(void)
 
 static inline void invoke_softirq(void)
 {
-	if (ksoftirqd_running(local_softirq_pending()))
+	if (ksoftirqd_running(softirq_pending_enabled()))
 		return;
 
 	if (!force_irqthreads) {
@@ -409,7 +410,7 @@ void irq_exit(void)
 #endif
 	account_irq_exit_time(current);
 	preempt_count_sub(HARDIRQ_OFFSET);
-	if (!in_interrupt() && local_softirq_pending())
+	if (!in_interrupt() && softirq_pending_enabled())
 		invoke_softirq();
 
 	tick_irq_exit();
@@ -640,13 +641,13 @@ void __init softirq_init(void)
 
 static int ksoftirqd_should_run(unsigned int cpu)
 {
-	return local_softirq_pending();
+	return softirq_pending_enabled();
 }
 
 static void run_ksoftirqd(unsigned int cpu)
 {
 	local_irq_disable();
-	if (local_softirq_pending()) {
+	if (softirq_pending_enabled()) {
 		/*
 		 * We can safely run softirq on inline stack, as we are not deep
 		 * in the task stack here.
-- 
2.17.1