linux-kernel - Re: [PATCH v4 3/6] smp: add function to execute a function synchronously on a cpu

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Message-ID: <20160405081107.GH3448@twins.programming.kicks-ass.net>
Date:	Tue, 5 Apr 2016 10:11:07 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Juergen Gross <jgross@...e.com>
Cc:	linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
	boris.ostrovsky@...cle.com, david.vrabel@...rix.com,
	mingo@...hat.com, Douglas_Warzecha@...l.com, pali.rohar@...il.com,
	jdelvare@...e.com, linux@...ck-us.net, tglx@...utronix.de,
	hpa@...or.com, jeremy@...p.org, chrisw@...s-sol.org,
	akataria@...are.com, rusty@...tcorp.com.au,
	virtualization@...ts.linux-foundation.org, x86@...nel.org
Subject: Re: [PATCH v4 3/6] smp: add function to execute a function
 synchronously on a cpu

On Tue, Apr 05, 2016 at 07:10:04AM +0200, Juergen Gross wrote:
> +int smp_call_on_cpu(unsigned int cpu, bool pin, int (*func)(void *), void *par)

Why .pin and not .phys? .pin does not (to me) reflect the
hypervisor/physical-cpu thing.

Also, as per smp_call_function_single() would it not be more consistent
to make this the last argument?

> +{
> +	struct smp_call_on_cpu_struct sscs = {
> +		.work = __WORK_INITIALIZER(sscs.work, smp_call_on_cpu_callback),
> +		.done = COMPLETION_INITIALIZER_ONSTACK(sscs.done),
> +		.func = func,
> +		.data = par,
> +		.cpu  = pin ? cpu : -1,
> +	};
> +
> +	if (cpu >= nr_cpu_ids)

You might want to also include cpu_online().

	if (cpu >= nr_cpu_ids || !cpu_online(cpu))
> +		return -ENXIO;

Seeing how its fairly hard to schedule work on a cpu that's not actually
there.

> +
> +	queue_work_on(cpu, system_wq, &sscs.work);
> +	wait_for_completion(&sscs.done);
> +
> +	return sscs.ret;
> +}