linux-kernel - [PATCH] softirq: wake up ktimer thread in softirq context

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Message-Id: <20221208075604.811710-1-junxiao.chang@intel.com>
Date:   Thu,  8 Dec 2022 15:56:04 +0800
From:   Junxiao Chang <junxiao.chang@...el.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-rt-users@...r.kernel.org, bigeasy@...utronix.de,
        tglx@...utronix.de, rostedt@...dmis.org, junxiao.chang@...el.com,
        hock.zhang.peh@...el.com
Subject: [PATCH] softirq: wake up ktimer thread in softirq context

Occiaionally timer interrupt might be triggered in softirq context,
ktimer thread should be woken up with RT kernel, or else ktimer
thread might stay in sleep state although timer interrupt has been
triggered.

This change fixes a latency issue that timer handler is delayed for
more than 4ms in network related test.

Fixes: 2165d27554e8 ("softirq: Use a dedicated thread for timer wakeups.")
Reported-by: Peh, Hock Zhang <hock.zhang.peh@...el.com>
Signed-off-by: Junxiao Chang <junxiao.chang@...el.com>
---
 kernel/softirq.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/kernel/softirq.c b/kernel/softirq.c
index ab1fe34326bab..34ae39e4a3d10 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -664,13 +664,10 @@ static inline void __irq_exit_rcu(void)
 #endif
 	account_hardirq_exit(current);
 	preempt_count_sub(HARDIRQ_OFFSET);
-	if (!in_interrupt()) {
-		if (local_softirq_pending())
-			invoke_softirq();
-
-		if (IS_ENABLED(CONFIG_PREEMPT_RT) && local_pending_timers())
-			wake_timersd();
-	}
+	if (!in_interrupt() && local_softirq_pending())
+		invoke_softirq();
+	if (!(in_nmi() || in_hardirq()) && local_pending_timers())
+		wake_timersd();
 
 	tick_irq_exit();
 }
-- 
2.25.1