linux-kernel - Re: [PATCH 3/5] irq_work: Implement remote queueing

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Message-ID: <1401812947.3645.231.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Tue, 03 Jun 2014 09:29:07 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kevin Hilman <khilman@...aro.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Viresh Kumar <viresh.kumar@...aro.org>
Subject: Re: [PATCH 3/5] irq_work: Implement remote queueing

On Tue, 2014-06-03 at 16:40 +0200, Frederic Weisbecker wrote:
> irq work currently only supports local callbacks. However its code
> is mostly ready to run remote callbacks and we have some potential user.
> 
> The full nohz subsystem currently open codes its own remote irq work
> on top of the scheduler ipi when it wants a CPU to reevaluate its next
> tick. However this ad hoc solution bloats the scheduler IPI.
> 
> Lets just extend the irq work subsystem to support remote queuing on top
> of the generic SMP IPI to handle this kind of user. This shouldn't add
> noticeable overhead.



>   */
> +bool irq_work_queue_on(struct irq_work *work, int cpu)
> +{
> +	/* All work should have been flushed before going offline */
> +	WARN_ON_ONCE(cpu_is_offline(cpu));
> +
> +	/* Arch remote IPI send/receive backend aren't NMI safe */
> +	WARN_ON_ONCE(in_nmi());
> +
> +	/* Only queue if not already pending */
> +	if (!irq_work_claim(work))
> +		return false;
> +
> +	if (llist_add(&work->llnode, &per_cpu(raised_list, cpu)))
> +		native_send_call_func_single_ipi(cpu);
> +
> +	return true;
> +}
> +EXPORT_SYMBOL_GPL(irq_work_queue_on);
> +

I am curious, this should only compile on x86, right ?



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