linux-kernel - Re: [PATCH RFC tip/core/rcu 2/5] srcu: Provide internal interface to start a Tiny SRCU grace period

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Date:   Fri, 20 Nov 2020 17:06:13 +0530
From:   Neeraj Upadhyay <neeraju@...eaurora.org>
To:     paulmck@...nel.org
Cc:     linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
        jiangshanlai@...il.com, akpm@...ux-foundation.org,
        mathieu.desnoyers@...icios.com, josh@...htriplett.org,
        tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
        dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com,
        oleg@...hat.com, joel@...lfernandes.org, rcu@...r.kernel.org
Subject: Re: [PATCH RFC tip/core/rcu 2/5] srcu: Provide internal interface to
 start a Tiny SRCU grace period



On 11/17/2020 6:10 AM, paulmck@...nel.org wrote:
> From: "Paul E. McKenney" <paulmck@...nel.org>
> 
> There is a need for a polling interface for SRCU grace periods.
> This polling needs to initiate an SRCU grace period without
> having to queue (and manage) a callback.  This commit therefore
> splits the Tiny SRCU call_srcu() function into callback-queuing and
> start-grace-period portions, with the latter in a new function named
> srcu_gp_start_if_needed().
> 
> Link: https://lore.kernel.org/rcu/20201112201547.GF3365678@moria.home.lan/
> Reported-by: Kent Overstreet <kent.overstreet@...il.com>
> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> ---

Reviewed-by: Neeraj Upadhyay <neeraju@...eaurora.org>


Thanks
Neeraj

>   kernel/rcu/srcutiny.c | 17 +++++++++++------
>   1 file changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
> index 5598cf6..3bac1db 100644
> --- a/kernel/rcu/srcutiny.c
> +++ b/kernel/rcu/srcutiny.c
> @@ -152,6 +152,16 @@ void srcu_drive_gp(struct work_struct *wp)
>   }
>   EXPORT_SYMBOL_GPL(srcu_drive_gp);
>   
> +static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
> +{
> +	if (!READ_ONCE(ssp->srcu_gp_running)) {
> +		if (likely(srcu_init_done))
> +			schedule_work(&ssp->srcu_work);
> +		else if (list_empty(&ssp->srcu_work.entry))
> +			list_add(&ssp->srcu_work.entry, &srcu_boot_list);
> +	}
> +}
> +
>   /*
>    * Enqueue an SRCU callback on the specified srcu_struct structure,
>    * initiating grace-period processing if it is not already running.
> @@ -167,12 +177,7 @@ void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
>   	*ssp->srcu_cb_tail = rhp;
>   	ssp->srcu_cb_tail = &rhp->next;
>   	local_irq_restore(flags);
> -	if (!READ_ONCE(ssp->srcu_gp_running)) {
> -		if (likely(srcu_init_done))
> -			schedule_work(&ssp->srcu_work);
> -		else if (list_empty(&ssp->srcu_work.entry))
> -			list_add(&ssp->srcu_work.entry, &srcu_boot_list);
> -	}
> +	srcu_gp_start_if_needed(ssp);
>   }
>   EXPORT_SYMBOL_GPL(call_srcu);
>   
> 

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