Subject: Re: [PATCH] net: Add napi_sycnhronize() to sync with napi poll

From: Josh Boyer <[email-masked]>
Date: Wed, 17 Oct 2007 20:02:03 -0500

On Thu, 2007-10-18 at 08:04 +1000, Benjamin Herrenschmidt wrote:
> net: Add __napi_synchronize() to sync with napi poll
> 
> The EMAC driver which needs to handle multiple devices with one
> NAPI instance implements its own per-channel disable bit. However,
> when setting such a bit, it needs to synchronize with the poller
> (that is make sure that any pending poller instance has completed,
> or is started late enough to see that disable bit).
> 
> This implements a low level __napi_synchronize() function to acheive
> that. The underscores are to emphasis the low level aspect of it and
> to discourage driver writers who don't know what they are doing to
> use it (to please DaveM :-)
> 
> Signed-off-by: Benjamin Herrenschmidt <[email-masked]>

Ok, trying again, leaving the actual patch below.  In the above patch
description, you still call it __napi_synchronize.  In the patch below,
it's napi_syncronize.

I was just trying to point out to whomever commits this patch that the
actual description should probably be fixed.

> ---
> 
> Back to msleep() since it fits my need well and that's what
> you used as well. Note that the smp_mb() will turn into barrier()
> on non-SMP.
> 
> I'll send a separate patch to fix EMAC to use the non __ version.
> 
> Index: linux-work/include/linux/netdevice.h
> ===================================================================
> --- linux-work.orig/include/linux/netdevice.h	2007-10-17 13:31:32.000000000 +1000
> +++ linux-work/include/linux/netdevice.h	2007-10-18 08:01:05.000000000 +1000
> @@ -394,6 +394,23 @@ static inline void napi_disable(struct n
>  }
> 
>  /**
> + *	napi_synchronize - synchronize with a concurrent poll
> + *	@n: napi context
> + *
> + * Synchronizes with a concurrent poll. Not to be used in normal
> + * drivers, mostly useful if you end up with multiple interfaces
> + * on one NAPI instance. This must be called from task context.
> + */
> +static inline void napi_synchronize(struct napi_struct *n)
> +{
> +	smp_mb();
> +#ifdef CONFIG_SMP
> +	while (test_bit(NAPI_STATE_SCHED, &n->state))
> +		msleep(1);
> +#endif /* CONFIG_SMP */
> +}
> +
> +/**
>   *	napi_enable - enable NAPI scheduling
>   *	@n: napi context
>   *
> 
> 
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