linux-kernel - Re: [PATCH v2 1/2] sched: Add cond_resched_rcu

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Message-ID: <alpine.LFD.2.00.1304301011310.1700@ja.ssi.bg>
Date:	Tue, 30 Apr 2013 10:12:38 +0300 (EEST)
From:	Julian Anastasov <ja@....bg>
To:	Simon Horman <horms@...ge.net.au>
cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	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>
Subject: Re: [PATCH v2 1/2] sched: Add cond_resched_rcu_lock() helper


	Hello,

On Tue, 30 Apr 2013, Simon Horman wrote:

> 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 call to cond_resched() is guarded by #ifndef CONFIG_PREEMPT_RCU as in
> the case of CONFIG_PREEMPT_RCU _rcu_read_unlock() will check to see if the
> RCU core needs to be informed, so there is no need to invoke cond_resched()
> in that case. Thanks to Paul E. McKenney for explaining this.
> 
> cond_resched_rcu_lock() suggested by Eric Dumazet.
> ifndef guard suggested by Paul E. McKenney and Julian Anastasov.
> 
> Cc: Eric Dumazet <eric.dumazet@...il.com>
> Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Cc: Julian Anastasov <ja@....bg>
> Acked-by: Ingo Molnar <mingo@...nel.org>
> Signed-off-by: Simon Horman <horms@...ge.net.au>
> 
> ---
> 
> v2
> * Add guard the call to cond_resched()
> ---
>  include/linux/sched.h | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index e692a02..66da71c 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -2787,3 +2787,14 @@ static inline unsigned long rlimit_max(unsigned int limit)
>  }
>  
>  #endif
> +
> +static void inline cond_resched_rcu_lock(void)
> +{
> +	if (need_resched()) {

	Ops, it should be without above need_resched.

> +		rcu_read_unlock();
> +#ifndef CONFIG_PREEMPT_RCU
> +		cond_resched();
> +#endif
> +		rcu_read_lock();
> +	}
> +}
> -- 
> 1.8.2.1

Regards

--
Julian Anastasov <ja@....bg>
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