Date: Mon, 16 May 2011 22:27:47 +0300 From: Andriy Gapon <avg@FreeBSD.org> To: John Baldwin <jhb@FreeBSD.org> 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 Message-ID: <4DD17AB3.1070606@FreeBSD.org> In-Reply-To: <201105161421.27665.jhb@freebsd.org> References: <4DCD357D.6000109@FreeBSD.org> <201105161152.10458.jhb@freebsd.org> <201105161346.34134.max@love2party.net> <201105161421.27665.jhb@freebsd.org>
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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
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