netdev - Re: NAPI poll behavior in various Intel drivers

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Message-ID: <20080107082413.GA1761@ff.dom.local>
Date:	Mon, 7 Jan 2008 09:24:13 +0100
From:	Jarek Poplawski <jarkao2@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, auke-jan.h.kok@...el.com
Subject: Re: NAPI poll behavior in various Intel drivers

On 04-01-2008 12:40, David Miller wrote:
...
> That "tx_cleaned" thing clouds the logic in all of these driver's
> poll routines.
> 
> The one necessary precondition is that when work_done < budget
> we exit polling and return a value less than budget.
> 
> If the ->poll() returns a value less than budget, net_rx_action()
> assumes that the device has been removed from the poll() list.
> 
> 		/* Drivers must not modify the NAPI state if they
> 		 * consume the entire weight.  In such cases this code
> 		 * still "owns" the NAPI instance and therefore can
> 		 * move the instance around on the list at-will.
> 		 */
> 		if (unlikely(work == weight))
> 			list_move_tail(&n->poll_list, list);
> 

Probably it's because of this clouded logic, but IMHO: "Drivers must
not modify the NAPI state if..." doesn't imply: drivers must modify
the NAPI state otherwise. (But it seems I must have missed the real
reason for this quote here.)

Regards,
Jarek P.
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