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Date: Mon, 16 May 2011 22:27:47 +0300
From: Andriy Gapon <avg@FreeBSD.org>
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To: John Baldwin <jhb@FreeBSD.org>
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Cc: Max Laier <max@love2party.net>,
	FreeBSD current <freebsd-current@FreeBSD.org>, neel@FreeBSD.org,
	Peter Grehan <grehan@FreeBSD.org>
Subject: Re: proposed smp_rendezvous change
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on 16/05/2011 21:21 John Baldwin said the following:
> How about this:
...
>  /* 
>   * Shared mutex to restrict busywaits between smp_rendezvous() and
> @@ -311,39 +312,62 @@ restart_cpus(cpumask_t map)
>  void
>  smp_rendezvous_action(void)
>  {
> -	void* local_func_arg = smp_rv_func_arg;
> -	void (*local_setup_func)(void*)   = smp_rv_setup_func;
> -	void (*local_action_func)(void*)   = smp_rv_action_func;
> -	void (*local_teardown_func)(void*) = smp_rv_teardown_func;
> +	void *local_func_arg;
> +	void (*local_setup_func)(void*);
> +	void (*local_action_func)(void*);
> +	void (*local_teardown_func)(void*);
> +	int generation;
>  
>  	/* Ensure we have up-to-date values. */
>  	atomic_add_acq_int(&smp_rv_waiters[0], 1);
>  	while (smp_rv_waiters[0] < smp_rv_ncpus)
>  		cpu_spinwait();
>  
> -	/* setup function */
> +	/* Fetch rendezvous parameters after acquire barrier. */
> +	local_func_arg = smp_rv_func_arg;
> +	local_setup_func = smp_rv_setup_func;
> +	local_action_func = smp_rv_action_func;
> +	local_teardown_func = smp_rv_teardown_func;

I want to ask once again - please pretty please convince me that the above
cpu_spinwait() loop is really needed and, by extension, that the assignments
should be moved behind it.
Please :)

-- 
Andriy Gapon