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Subject: Re: [PATCH/RFC] net: Add __napi_sycnhronize() to sync with napi poll
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Stephen Hemminger <shemminger@linux-foundation.org>
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Date: Thu, 18 Oct 2007 07:52:32 +1000
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Cc: netdev@vger.kernel.org, Roland Dreier <rdreier@cisco.com>,
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On Wed, 2007-10-17 at 08:31 -0700, Stephen Hemminger wrote:
> Please don't use double underscore, for this function name. There is no
> reason to not make it a normal API call.
> 
> The sky2 fix I am working on will use napi_synchronize as well.

Allright. A compiler barrier in the !SMP case makes sense, but I would
still want an smp_mb() before the test_bit. I think it's a bug in
synchronize_irq not to have it.

Cheers,
Ben.
 
> --- a/include/linux/netdevice.h	2007-10-16 16:48:20.000000000 -0700
> +++ b/include/linux/netdevice.h	2007-10-17 08:29:55.000000000 -0700
> @@ -407,6 +407,24 @@ static inline void napi_enable(struct na
>  	clear_bit(NAPI_STATE_SCHED, &n->state);
>  }
>  
> +#ifdef CONFIG_SMP
> +/**
> + *	napi_synchronize - wait until NAPI is not running
> + *	@n: napi context
> + *
> + * Wait until NAPI is done being scheduled on this context.
> + * Any outstanding processing completes but
> + * does not disable future activations.
> + */
> +static inline void napi_synchronize(const struct napi_struct *n)
> +{
> +	while (test_bit(NAPI_STATE_SCHED, &n->state))
> +		msleep(1);
> +}
> +#else
> +# define napi_synchronize(n)	barrier()
> +#endif
> +
>  /*
>   *	The DEVICE structure.
>   *	Actually, this whole structure is a big mistake.  It mixes I/O