linux-kernel - Re: [PATCH 2/2] rcu: Force resched_cpu when jiffies >= rcu_state.jiffies

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Date:   Tue, 22 Nov 2016 17:12:20 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     paulmck@...ux.vnet.ibm.com, josh@...htriplett.org,
        rostedt@...dmis.org, mathieu.desnoyers@...icios.com,
        jiangshanlai@...il.com
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] rcu: Force resched_cpu when jiffies >=
 rcu_state.jiffies_resched

On Wed, Nov 09, 2016 at 03:32:15PM +0900, Byungchul Park wrote:
> Currently rcu code forces CPU into scheduler when jiffies >=
> rcu_state.gp_start + jiffies_till_sched_qs, via resched_cpu().
> 
> It would be better to force CPU into scheduler when jiffies >=
> rcu_state.jiffies_resched, too.

Hello,

I think these two patches are necessary to call resched_cpu() even in
case of jiffies >= rcu_state.jiffies_resched, too. Am I wrong?

It would be appriciated if you let me know if I was wrong.

Thank you,
Byungchul

> 
> Signed-off-by: Byungchul Park <byungchul.park@....com>
> ---
>  kernel/rcu/tree.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index d8e8859..287f468 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -1217,11 +1217,10 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
>  				   READ_ONCE(*rcrmp) + rdp->rsp->flavor_mask);
>  		}
>  		rdp->rsp->jiffies_resched += 5; /* Re-enable beating. */
> -	}
>  
> -	/* And if it has been a really long time, kick the CPU as well. */
> -	if (ULONG_CMP_GE(jiffies, rdp->rsp->gp_start + jiffies_till_sched_qs))
> +		/* And if it has been a really long time, kick the CPU as well. */
>  		resched_cpu(rdp->cpu);  /* Force CPU into scheduler. */
> +	}
>  
>  	return 0;
>  }
> -- 
> 1.9.1