linux-kernel - Re: [PATCH rcu 2/3] doc: Document the rcutree.rcu

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Message-ID: <a40ab401-1368-b287-0e2b-daf8026bbf5a@quicinc.com>
Date:   Tue, 21 Jun 2022 10:40:54 +0530
From:   Neeraj Upadhyay <quic_neeraju@...cinc.com>
To:     "Paul E. McKenney" <paulmck@...nel.org>, <rcu@...r.kernel.org>
CC:     <linux-kernel@...r.kernel.org>, <kernel-team@...com>,
        <rostedt@...dmis.org>, Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH rcu 2/3] doc: Document the rcutree.rcu_divisor kernel boot
 parameter



On 6/21/2022 3:47 AM, Paul E. McKenney wrote:
> This commit adds kernel-parameters.txt documentation for the
> rcutree.rcu_divisor kernel boot parameter, which controls the softirq
> callback-invocation batch limit.
> 
> Cc: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> ---

Reviewed-by: Neeraj Upadhyay <quic_neeraju@...cinc.com>

>   Documentation/admin-guide/kernel-parameters.txt | 15 +++++++++++++++
>   1 file changed, 15 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 2522b11e593f2..bdf431bdbfdc4 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -4666,6 +4666,21 @@
>   			When RCU_NOCB_CPU is set, also adjust the
>   			priority of NOCB callback kthreads.
>   
> +	rcutree.rcu_divisor= [KNL]
> +			Set the shift-right count to use to compute
> +			the callback-invocation batch limit bl from
> +			the number of callbacks queued on this CPU.
> +			The result will be bounded below by the value of
> +			the rcutree.blimit kernel parameter.  Every bl
> +			callbacks, the softirq handler will exit in
> +			order to allow the CPU to do other work.
> +
> +			Please note that this callback-invocation batch
> +			limit applies only to non-offloaded callback
> +			invocation.  Offloaded callbacks are instead
> +			invoked in the context of an rcuoc kthread, which
> +			scheduler will preempt as it does any other task.
> +
>   	rcutree.rcu_nocb_gp_stride= [KNL]
>   			Set the number of NOCB callback kthreads in
>   			each group, which defaults to the square root