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SubjectRe: [patch 1/4] x86, mtrr: lock stop machine during MTRR rendezvous sequence
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On Wed, 2011-06-22 at 15:20 -0700, Suresh Siddha wrote:
> +#ifdef CONFIG_SMP
> + /*
> + * If we are not yet online, then there can be no stop_machine() in
> + * parallel. Stop machine ensures this by using get_online_cpus().
> + *
> + * If we are online, then we need to prevent a stop_machine() happening
> + * in parallel by taking the stop cpus mutex.
> + */
> + if (cpu_online(raw_smp_processor_id()))
> + mutex_lock(&stop_cpus_mutex);
> +#endif

This reads like an optimization, is it really worth-while to not take
the mutex in the rare offline case?


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