linux-kernel - [RFC PATCH 3/4] softirq: Defer to workqueue when rescheduling is needed

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Date:   Fri, 19 Jan 2018 16:46:13 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        Levin Alexander <alexander.levin@...izon.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Mauro Carvalho Chehab <mchehab@...pensource.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Dmitry Safonov <dima@...sta.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Radu Rendec <rrendec@...sta.com>,
        Ingo Molnar <mingo@...nel.org>,
        Stanislaw Gruszka <sgruszka@...hat.com>,
        Rik van Riel <riel@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        David Miller <davem@...emloft.net>
Subject: [RFC PATCH 3/4] softirq: Defer to workqueue when rescheduling is needed

One more step toward converting ksoftirqd to per vector workqueues.

Suggested-by: Paolo Abeni <pabeni@...hat.com>
Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Cc: Dmitry Safonov <dima@...sta.com>
Cc: Eric Dumazet <edumazet@...gle.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: David Miller <davem@...emloft.net>
Cc: Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Levin Alexander <alexander.levin@...izon.com>
Cc: Paolo Abeni <pabeni@...hat.com>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Radu Rendec <rrendec@...sta.com>
Cc: Rik van Riel <riel@...hat.com>
Cc: Stanislaw Gruszka <sgruszka@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Wanpeng Li <wanpeng.li@...mail.com>
Cc: Mauro Carvalho Chehab <mchehab@...pensource.com>
---
 kernel/softirq.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/kernel/softirq.c b/kernel/softirq.c
index becb1d9..bb0cffa 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -369,16 +369,14 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
 
 	pending = local_softirq_pending() & ~softirq->pending_work_mask;
 	if (pending) {
-		if (need_resched()) {
-			wakeup_softirqd();
-		} else {
-			/* Vectors that got re-enqueued are threaded */
-			if (executed & pending)
-				do_softirq_workqueue(executed & pending);
-			pending &= ~executed;
-			if (pending)
-				goto restart;
-		}
+		if (need_resched())
+			executed = pending;
+		/* Vectors that got re-enqueued are threaded */
+		if (executed & pending)
+			do_softirq_workqueue(executed & pending);
+		pending &= ~executed;
+		if (pending)
+			goto restart;
 	}
 
 	lockdep_softirq_end(in_hardirq);
-- 
2.7.4