linux-kernel - [RFC PATCH 1/1] Softirq:avoid large sched delay from the pending softirqs

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Message-Id: <1594967873-29522-1-git-send-email-qianjun.kernel@gmail.com>
Date:   Fri, 17 Jul 2020 02:37:53 -0400
From:   qianjun.kernel@...il.com
To:     tglx@...utronix.de, peterz@...radead.org, will@...nel.org,
        luto@...nel.org
Cc:     linux-kernel@...r.kernel.org, shaoyafang@...iglobal.com,
        jun qian <qianjun.kernel@...il.com>
Subject: [RFC PATCH 1/1] Softirq:avoid large sched delay from the pending softirqs

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

When get the pending softirqs, it need to process all the pending
softirqs in the while loop. If the processing time of each pending
softirq is need more than 2 msec in this loop, or one of the softirq
will running a long time, according to the original code logic, it
will process all the pending softirqs without wakeuping ksoftirqd,
which will cause a relatively large scheduling delay on the
corresponding CPU, which we do not wish to see. The patch will check
the total time to process pending softirq, if the time exceeds 2 ms
we need to wakeup the ksofirqd to aviod large sched delay.

Signed-off-by: jun qian <qianjun.kernel@...il.com>
---
 kernel/softirq.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/softirq.c b/kernel/softirq.c
index c4201b7f..602d9fa 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -299,6 +299,9 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
 		}
 		h++;
 		pending >>= softirq_bit;
+
+		if (time_after(jiffies, end) && need_resched())
+			break;
 	}

 	if (__this_cpu_read(ksoftirqd) == current)
-- 
1.8.3.1