From: Peter Zijlstra <peterz@infradead.org>
To: Julian Anastasov <ja@ssi.bg>
Cc: Simon Horman <horms@verge.net.au>,
Eric Dumazet <eric.dumazet@gmail.com>,
Ingo Molnar <mingo@redhat.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
lvs-devel@vger.kernel.org, netdev@vger.kernel.org,
netfilter-devel@vger.kernel.org, linux-kernel@vger.kernel.org,
Pablo Neira Ayuso <pablo@netfilter.org>,
Dipankar Sarma <dipankar@in.ibm.com>
Subject: Re: [PATCH v2 1/2] sched: Add cond_resched_rcu_lock() helper
Date: Wed, 1 May 2013 17:55:02 +0200 [thread overview]
Message-ID: <20130501155501.GB7521@dyad.programming.kicks-ass.net> (raw)
In-Reply-To: <alpine.LFD.2.00.1305011344320.1603@ja.ssi.bg>
On Wed, May 01, 2013 at 05:22:05PM +0300, Julian Anastasov wrote:
> > static void inline cond_resched_rcu_lock(void)
> > {
> > #ifdef CONFIG_PREEMPT_RCU
>
> You mean '#ifndef' here, right? But in the non-preempt
> case is using the need_resched() needed? rcu_read_unlock
> and rcu_read_lock do not generate code.
Uhm... yes!
> > if (need_resched()) {
> > rcu_read_unlock();
> > cond_resched();
> > rcu_read_lock();
> > }
> > #endif /* CONFIG_PREEMPT_RCU */
> > }
> >
> > That would have an rcu_read_lock() break and voluntary preemption point for
> > non-preemptible RCU and not bother with the stuff for preemptible RCU.
>
> I see. So, can we choose one of both variants:
>
> 1. Your variant but with ifndef:
>
> static void inline cond_resched_rcu_lock(void)
> {
> #ifndef CONFIG_PREEMPT_RCU
> if (need_resched()) {
> rcu_read_unlock();
> cond_resched();
> rcu_read_lock();
> }
> #endif
> }
>
> 2. Same without need_resched because cond_resched already
> performs the same checks:
>
> static void inline cond_resched_rcu_lock(void)
> {
> #ifndef CONFIG_PREEMPT_RCU
> rcu_read_unlock();
> cond_resched();
> rcu_read_lock();
> #endif
> }
Ah so the 'problem' with this last version is that it does an unconditional /
unnessecary rcu_read_unlock().
The below would be in line with all the other cond_resched*() implementations.
---
include/linux/sched.h | 7 +++++++
kernel/sched/core.c | 14 ++++++++++++++
2 files changed, 21 insertions(+)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 802a751..fd2c77f 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2449,6 +2449,13 @@ extern int __cond_resched_softirq(void);
__cond_resched_softirq(); \
})
+extern int __cond_resched_rcu(void);
+
+#define cond_resched_rcu() ({ \
+ __might_sleep(__FILE__, __LINE__, 0); \
+ __cond_resched_rcu(); \
+})
+
/*
* Does a critical section need to be broken due to another
* task waiting?: (technically does not depend on CONFIG_PREEMPT,
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 7d7901a..2b3b4e6 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4358,6 +4358,20 @@ int __sched __cond_resched_softirq(void)
}
EXPORT_SYMBOL(__cond_resched_softirq);
+int __sched __cond_resched_rcu(void)
+{
+#ifndef CONFIG_PREEMPT_RCU
+ if (should_resched()) {
+ rcu_read_unlock();
+ __cond_resched();
+ rcu_read_lock();
+ return 1;
+ }
+#endif
+ return 0;
+}
+EXPORT_SYMBOL(__cond_resched_rcu);
+
/**
* yield - yield the current processor to other threads.
*
next prev parent reply other threads:[~2013-05-01 15:55 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-04-30 2:52 [PATCH v2 0/2] sched: Add cond_resched_rcu_lock() helper Simon Horman
2013-04-30 2:52 ` [PATCH v2 1/2] " Simon Horman
2013-04-30 7:12 ` Julian Anastasov
2013-04-30 7:29 ` Simon Horman
2013-04-30 7:52 ` Julian Anastasov
2013-05-01 9:10 ` Peter Zijlstra
2013-05-01 12:46 ` Paul E. McKenney
2013-05-01 14:32 ` Paul E. McKenney
2013-05-02 7:27 ` Peter Zijlstra
2013-05-01 15:17 ` Peter Zijlstra
2013-05-01 15:29 ` Eric Dumazet
2013-05-01 15:59 ` Peter Zijlstra
2013-05-01 16:02 ` Paul E. McKenney
2013-05-01 16:57 ` Peter Zijlstra
2013-05-01 17:30 ` Paul E. McKenney
2013-05-01 14:22 ` Julian Anastasov
2013-05-01 15:55 ` Peter Zijlstra [this message]
2013-05-01 18:22 ` Julian Anastasov
2013-05-01 19:04 ` Paul E. McKenney
2013-05-02 7:26 ` Peter Zijlstra
2013-05-02 10:06 ` Julian Anastasov
2013-05-02 15:54 ` Julian Anastasov
2013-05-02 17:32 ` Paul E. McKenney
2013-05-02 18:55 ` Julian Anastasov
2013-05-02 19:24 ` Julian Anastasov
2013-05-02 19:34 ` Paul E. McKenney
2013-05-02 20:19 ` Julian Anastasov
2013-05-02 22:31 ` Paul E. McKenney
2013-05-03 7:52 ` Julian Anastasov
2013-05-03 16:30 ` Paul E. McKenney
2013-05-03 17:04 ` Peter Zijlstra
2013-05-03 17:34 ` Paul E. McKenney
2013-05-03 18:09 ` Peter Zijlstra
2013-05-03 17:47 ` Julian Anastasov
2013-05-04 7:23 ` Julian Anastasov
2013-05-04 18:03 ` Paul E. McKenney
2013-04-30 2:52 ` [PATCH v2 2/2] ipvs: Use cond_resched_rcu_lock() helper when dumping connections Simon Horman
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