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Date: Wed, 22 May 2013 14:50:31 +0900 From: Simon Horman <horms@...ge.net.au> To: Eric Dumazet <eric.dumazet@...il.com>, Julian Anastasov <ja@....bg>, Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Cc: lvs-devel@...r.kernel.org, netdev@...r.kernel.org, netfilter-devel@...r.kernel.org, linux-kernel@...r.kernel.org, Pablo Neira Ayuso <pablo@...filter.org>, Dipankar Sarma <dipankar@...ibm.com>, Simon Horman <horms@...ge.net.au> Subject: [PATCH ipvs-next v3 1/2] sched: add cond_resched_rcu() helper This is intended for use in loops which read data protected by RCU and may have a large number of iterations. Such an example is dumping the list of connections known to IPVS: ip_vs_conn_array() and ip_vs_conn_seq_next(). The benefits are for CONFIG_PREEMPT_RCU=y where we save CPU cycles by moving rcu_read_lock and rcu_read_unlock out of large loops but still allowing the current task to be preempted after every loop iteration for the CONFIG_PREEMPT_RCU=n case. The call to cond_resched() is not needed when CONFIG_PREEMPT_RCU=y. Thanks to Paul E. McKenney for explaining this and for the final version that checks the context with CONFIG_DEBUG_ATOMIC_SLEEP=y for all possible configurations. The function can be empty in the CONFIG_PREEMPT_RCU case, rcu_read_lock and rcu_read_unlock are not needed in this case because the task can be preempted on indication from scheduler. Thanks to Peter Zijlstra for catching this and for his help in trying a solution that changes __might_sleep. Initial cond_resched_rcu_lock() function suggested by Eric Dumazet. Tested-by: Julian Anastasov <ja@....bg> Signed-off-by: Julian Anastasov <ja@....bg> Signed-off-by: Simon Horman <horms@...ge.net.au> --- include/linux/sched.h | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/include/linux/sched.h b/include/linux/sched.h index e692a02..2080446 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2608,6 +2608,15 @@ extern int __cond_resched_softirq(void); __cond_resched_softirq(); \ }) +static inline void cond_resched_rcu(void) +{ +#if defined(CONFIG_DEBUG_ATOMIC_SLEEP) || !defined(CONFIG_PREEMPT_RCU) + rcu_read_unlock(); + cond_resched(); + rcu_read_lock(); +#endif +} + /* * Does a critical section need to be broken due to another * task waiting?: (technically does not depend on CONFIG_PREEMPT, -- 1.8.2.1 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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