On Wed, Jun 05, 2013 at 10:40:27PM +0200, Pablo Neira Ayuso wrote:
> From: Simon Horman <horms@xxxxxxxxxxxx>
>
> 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@xxxxxx>
> Signed-off-by: Julian Anastasov <ja@xxxxxx>
> Signed-off-by: Simon Horman <horms@xxxxxxxxxxxx>
> Acked-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> ---
> include/linux/sched.h | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 178a8d9..4ff8da1 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -2444,6 +2444,15 @@ 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,
> --
> 1.7.10.4
>
> --
> To unsubscribe from this list: send the line "unsubscribe netdev" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html
>
--
To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
