linux-kernel - Re: [patch 3/4] stop_machine: implement stop_machine_from_offline

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Date:	Thu, 23 Jun 2011 11:25:19 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	mingo@...e.hu, tglx@...utronix.de, hpa@...or.com, trenn@...ell.com,
	prarit@...hat.com, tj@...nel.org, rusty@...tcorp.com.au,
	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	linux-kernel@...r.kernel.org, youquan.song@...el.com
Subject: Re: [patch 3/4] stop_machine: implement
 stop_machine_from_offline_cpu()

On Wed, 2011-06-22 at 15:20 -0700, Suresh Siddha wrote:
> +int stop_machine_from_offline_cpu(int (*fn)(void *), void *data,
> +                                 const struct cpumask *cpus)
> +{
> +       struct stop_machine_data smdata = { .fn = fn, .data = data,
> +                                           .active_cpus = cpus };
> +       struct cpu_stop_done done;
> +       int ret;
> +
> +       /* Local CPU must be offline and CPU hotplug in progress. */
> +       BUG_ON(cpu_online(raw_smp_processor_id()));
> +       smdata.num_threads = num_online_cpus() + 1;     /* +1 for local */
> +
> +       /* No proper task established and can't sleep - busy wait for lock. */
> +       while (!mutex_trylock(&stop_cpus_mutex))
> +               cpu_relax();
> +
> +       /* Schedule work on other CPUs and execute directly for local CPU */
> +       set_state(&smdata, STOPMACHINE_PREPARE);
> +       cpu_stop_init_done(&done, num_online_cpus());
> +       queue_stop_cpus_work(cpu_online_mask, stop_machine_cpu_stop, &smdata,
> +                            &done);
> +       ret = stop_machine_cpu_stop(&smdata);
> +
> +       /* Busy wait for completion. */
> +       while (!completion_done(&done.completion))
> +               cpu_relax();
> +
> +       mutex_unlock(&stop_cpus_mutex);
> +       return ret ?: done.ret;
> +} 

Damn thats ugly, I sure hope you're going to make those hardware folks
pay for this :-)

In commit d0af9eed5aa91b6b7b5049cae69e5ea956fd85c3 you mention that its
specific to HT, wouldn't it make sense to limit the stop-machine use in
the next patch to the sibling mask instead of the whole machine?
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