linux-kernel - [PATCH tip/core/rcu 01/22] sched: Make non-production PREEMPT cond

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Message-Id: <1524450747-22778-1-git-send-email-paulmck@linux.vnet.ibm.com>
Date:   Sun, 22 Apr 2018 19:32:06 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel.opensrc@...il.com,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 01/22] sched: Make non-production PREEMPT cond_resched() help Tasks RCU

In CONFIG_PREEMPT=y kernels, cond_resched() is a complete no-op, and
thus cannot help advance Tasks-RCU grace periods.  However, such grace
periods are only an issue in non-production benchmarking runs of the
Linux kernel.  This commit therefore makes cond_resched() invoke
rcu_note_voluntary_context_switch() for kernels implementing Tasks RCU
even in CONFIG_PREEMPT=y kernels.

Reported-by: Steven Rostedt <rostedt@...dmis.org>
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 include/linux/sched.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index b3d697f3b573..fe8f7178a22d 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1617,6 +1617,12 @@ static inline int test_tsk_need_resched(struct task_struct *tsk)
  */
 #ifndef CONFIG_PREEMPT
 extern int _cond_resched(void);
+#elif defined(CONFIG_TRACEPOINT_BENCHMARK)
+static inline int _cond_resched(void)
+{
+	rcu_note_voluntary_context_switch(current);
+	return 0;
+}
 #else
 static inline int _cond_resched(void) { return 0; }
 #endif
-- 
2.5.2