linux-kernel - [PATCH 5/9] softirq: Context aware timeout

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Date:   Fri, 5 May 2023 19:33:11 +0800
From:   Liu Jian <liujian56@...wei.com>
To:     <corbet@....net>, <paulmck@...nel.org>, <frederic@...nel.org>,
        <quic_neeraju@...cinc.com>, <joel@...lfernandes.org>,
        <josh@...htriplett.org>, <boqun.feng@...il.com>,
        <rostedt@...dmis.org>, <mathieu.desnoyers@...icios.com>,
        <jiangshanlai@...il.com>, <qiang1.zhang@...el.com>,
        <jstultz@...gle.com>, <tglx@...utronix.de>, <sboyd@...nel.org>,
        <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <peterz@...radead.org>, <frankwoo@...gle.com>,
        <Rhinewuwu@...gle.com>
CC:     <liujian56@...wei.com>, <linux-doc@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <rcu@...r.kernel.org>,
        <netdev@...r.kernel.org>
Subject: [PATCH 5/9] softirq: Context aware timeout

From: Peter Zijlstra <peterz@...radead.org>

Reduce the softirq timeout when it is preempting an RT task.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Liu Jian <liujian56@...wei.com>
---
 kernel/softirq.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/kernel/softirq.c b/kernel/softirq.c
index e2cad5d108c8..baa08ae1604f 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -522,12 +522,12 @@ static inline void lockdep_softirq_end(bool in_hardirq) { }
 #define MAX_SOFTIRQ_TIME	(2 * NSEC_PER_MSEC)
 #define MAX_SOFTIRQ_RESTART	10
 
-static inline bool __softirq_needs_break(u64 start)
+static inline bool __softirq_needs_break(u64 start, u64 timo)
 {
 	if (need_resched())
 		return true;
 
-	if (sched_clock() - start >= MAX_SOFTIRQ_TIME)
+	if (sched_clock() - start >= timo)
 		return true;
 
 	return false;
@@ -537,6 +537,7 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
 {
 	unsigned int max_restart = MAX_SOFTIRQ_RESTART;
 	unsigned long old_flags = current->flags;
+	u64 timo = MAX_SOFTIRQ_TIME;
 	u64 start = sched_clock();
 	struct softirq_action *h;
 	unsigned long pending;
@@ -556,6 +557,9 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
 	in_hardirq = lockdep_softirq_start();
 	account_softirq_enter(current);
 
+	if (__this_cpu_read(ksoftirqd) != current && task_is_realtime(current))
+		timo >>= 2;
+
 restart:
 	/* Reset the pending bitmask before enabling irqs */
 	set_softirq_pending(0);
@@ -583,7 +587,7 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
 			preempt_count_set(prev_count);
 		}
 
-		if (pending && __softirq_needs_break(start))
+		if (pending && __softirq_needs_break(start, timo))
 			break;
 	}
 
@@ -596,7 +600,7 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
 	if (pending)
 		or_softirq_pending(pending);
 	else if ((pending = local_softirq_pending()) &&
-		 !__softirq_needs_break(start) &&
+		 !__softirq_needs_break(start, timo) &&
 		 --max_restart)
 		goto restart;
 
-- 
2.34.1