linux-kernel - [PATCH V7 2/4] softirq: Factor loop termination condition

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Message-Id: <20200915115609.85106-3-qianjun.kernel@gmail.com>
Date:   Tue, 15 Sep 2020 19:56:07 +0800
From:   qianjun.kernel@...il.com
To:     tglx@...utronix.de, peterz@...radead.org, will@...nel.org,
        luto@...nel.org, linux-kernel@...r.kernel.org
Cc:     laoar.shao@...il.com, qais.yousef@....com, urezki@...il.com,
        jun qian <qianjun.kernel@...il.com>
Subject: [PATCH V7 2/4] softirq: Factor loop termination condition

From: jun qian <qianjun.kernel@...il.com>

Add a function interface to end softirq process

Signed-off-by: jun qian <qianjun.kernel@...il.com>
---
 kernel/softirq.c | 44 +++++++++++++++++++++++++-------------------
 1 file changed, 25 insertions(+), 19 deletions(-)

diff --git a/kernel/softirq.c b/kernel/softirq.c
index 0db77ab..5a627cd 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -198,22 +198,6 @@ void __local_bh_enable_ip(unsigned long ip, unsigned int cnt)
 }
 EXPORT_SYMBOL(__local_bh_enable_ip);
 
-/*
- * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times,
- * but break the loop if need_resched() is set or after 2 ms.
- * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in
- * certain cases, such as stop_machine(), jiffies may cease to
- * increment and so we need the MAX_SOFTIRQ_RESTART limit as
- * well to make sure we eventually return from this method.
- *
- * These limits have been established via experimentation.
- * The two things to balance is latency against fairness -
- * we want to handle softirqs as soon as possible, but they
- * should not be able to lock up the box.
- */
-#define MAX_SOFTIRQ_TIME	(2 * NSEC_PER_MSEC)
-#define MAX_SOFTIRQ_RESTART 10
-
 #ifdef CONFIG_TRACE_IRQFLAGS
 /*
  * When we run softirqs from irq_exit() and thus on the hardirq stack we need
@@ -247,11 +231,34 @@ static inline void lockdep_softirq_end(bool in_hardirq)
 static inline void lockdep_softirq_end(bool in_hardirq) { }
 #endif
 
+/*
+ * We restart softirq processing but break the loop if need_resched() is
+ * set or after 2 ms. The MAX_SOFTIRQ_RESTART guarantees a loop termination
+ * if sched_clock() were ever to stall.
+ *
+ * These limits have been established via experimentation.  The two things
+ * to balance is latency against fairness - we want to handle softirqs as
+ * soon as possible, but they should not be able to lock up the box.
+ */
+#define MAX_SOFTIRQ_TIME	(2 * NSEC_PER_MSEC)
+#define MAX_SOFTIRQ_RESTART    10
+
+static inline bool __softirq_needs_break(u64 start)
+{
+	if (need_resched())
+		return true;
+
+	if (sched_clock() - start >= MAX_SOFTIRQ_TIME)
+		return true;
+
+	return false;
+}
+
 asmlinkage __visible void __softirq_entry __do_softirq(void)
 {
 	u64 start = sched_clock();
 	unsigned long old_flags = current->flags;
-	int max_restart = MAX_SOFTIRQ_RESTART;
+	unsigned int max_restart = MAX_SOFTIRQ_RESTART;
 	struct softirq_action *h;
 	bool in_hardirq;
 	__u32 pending;
@@ -308,8 +315,7 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
 
 	pending = local_softirq_pending();
 	if (pending) {
-		if (sched_clock() - start < MAX_SOFTIRQ_TIME && !need_resched() &&
-		    --max_restart)
+		if (!__softirq_needs_break(start) && --max_restart)
 			goto restart;
 
 		wakeup_softirqd();
-- 
1.8.3.1