linux-kernel - Re: [RFC PATCH 2/6] Preempt-RCU: Reorganize RCU code into rcuclassic.c and rcupdate.c

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Message-ID: <x7fxy572jh.fsf@saeurebad.de>
Date:	Fri, 14 Dec 2007 15:51:14 +0100
From:	Johannes Weiner <hannes-kernel@...urebad.de>
To:	ego@...ibm.com
Cc:	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Paul E McKenney <paulmck@...ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Ted Tso <tytso@...ibm.com>, dvhltc@...ibm.com,
	Oleg Nesterov <oleg@...sign.ru>,
	Andrew Morton <akpm@...ux-foundation.org>, bunk@...nel.org,
	Josh Triplett <josh@...edesktop.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [RFC PATCH 2/6] Preempt-RCU: Reorganize RCU code into rcuclassic.c and rcupdate.c

Hi,

Gautham R Shenoy <ego@...ibm.com> writes:

> diff --git a/kernel/rcuclassic.c b/kernel/rcuclassic.c
> new file mode 100644
> index 0000000..11c16aa
> --- /dev/null
> +++ b/kernel/rcuclassic.c
> +/**
> + * call_rcu - Queue an RCU callback for invocation after a grace period.
> + * @head: structure to be used for queueing the RCU updates.
> + * @func: actual update function to be invoked after the grace period
> + *
> + * The update function will be invoked some time after a full grace
> + * period elapses, in other words after all currently executing RCU
> + * read-side critical sections have completed.  RCU read-side critical
> + * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
> + * and may be nested.
> + */
> +void call_rcu(struct rcu_head *head,
> +				void (*func)(struct rcu_head *rcu))
> +{
> +	unsigned long flags;
> +	struct rcu_data *rdp;
> +
> +	head->func = func;
> +	head->next = NULL;
> +	local_irq_save(flags);
> +	rdp = &__get_cpu_var(rcu_data);
> +	*rdp->nxttail = head;
> +	rdp->nxttail = &head->next;
> +	if (unlikely(++rdp->qlen > qhimark)) {
> +		rdp->blimit = INT_MAX;
> +		force_quiescent_state(rdp, &rcu_ctrlblk);
> +	}
> +	local_irq_restore(flags);
> +}
> +EXPORT_SYMBOL_GPL(call_rcu);
> +
> +/**
> + * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
> + * @head: structure to be used for queueing the RCU updates.
> + * @func: actual update function to be invoked after the grace period
> + *
> + * The update function will be invoked some time after a full grace
> + * period elapses, in other words after all currently executing RCU
> + * read-side critical sections have completed. call_rcu_bh() assumes
> + * that the read-side critical sections end on completion of a softirq
> + * handler. This means that read-side critical sections in process
> + * context must not be interrupted by softirqs. This interface is to be
> + * used when most of the read-side critical sections are in softirq context.
> + * RCU read-side critical sections are delimited by rcu_read_lock() and
> + * rcu_read_unlock(), * if in interrupt context or rcu_read_lock_bh()
> + * and rcu_read_unlock_bh(), if in process context. These may be nested.
> + */
> +void call_rcu_bh(struct rcu_head *head,
> +				void (*func)(struct rcu_head *rcu))
> +{
> +	unsigned long flags;
> +	struct rcu_data *rdp;
> +
> +	head->func = func;
> +	head->next = NULL;
> +	local_irq_save(flags);
> +	rdp = &__get_cpu_var(rcu_bh_data);
> +	*rdp->nxttail = head;
> +	rdp->nxttail = &head->next;
> +
> +	if (unlikely(++rdp->qlen > qhimark)) {
> +		rdp->blimit = INT_MAX;
> +		force_quiescent_state(rdp, &rcu_bh_ctrlblk);
> +	}
> +
> +	local_irq_restore(flags);
> +}
> +EXPORT_SYMBOL_GPL(call_rcu_bh);

Those two functions are identical beside the difference of `rcu_data'
<-> `rcu_bh_data' and `rcu_ctrlblk' <-> `rcu_bh_ctrlblk'.

Is there a way to collapse the code into one helper function or would
that effect performance too much?

	Hannes
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