linux-kernel - Re: [PATCH v2 -next] rcu: rcu_qs -- Use raise_softirq

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Date:   Thu, 24 Jan 2019 12:59:27 -0800
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     Cyrill Gorcunov <gorcunov@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 -next] rcu: rcu_qs -- Use raise_softirq_irqoff to not
 save irqs twice

On Thu, Jan 24, 2019 at 09:14:37PM +0300, Cyrill Gorcunov wrote:
> The rcu_qs is disabling IRQs by self so no need to do the same in raise_softirq
> but instead we can save some cycles using raise_softirq_irqoff directly.
> 
> CC: Paul E. McKenney <paulmck@...ux.ibm.com>
> Signed-off-by: Cyrill Gorcunov <gorcunov@...il.com>

Good eyes, good combo optimization of both space and time, thank you!!!

Queued, most likely for v5.2.

							Thanx, Paul

> ---
> The prev patch body has been screwed, sorry.
> 
>  kernel/rcu/tiny.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: linux-next.git/kernel/rcu/tiny.c
> ===================================================================
> --- linux-next.git.orig/kernel/rcu/tiny.c
> +++ linux-next.git/kernel/rcu/tiny.c
> @@ -65,7 +65,7 @@ void rcu_qs(void)
>  	local_irq_save(flags);
>  	if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
>  		rcu_ctrlblk.donetail = rcu_ctrlblk.curtail;
> -		raise_softirq(RCU_SOFTIRQ);
> +		raise_softirq_irqoff(RCU_SOFTIRQ);
>  	}
>  	local_irq_restore(flags);
>  }
>