netdev - Re: [net-next PATCH 2/6] enic: Bug fix: try harder to fill Rx ring on skb allocation failures

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Message-ID: <C752BE07.1B019%scofeldm@cisco.com>
Date:	Sat, 19 Dec 2009 17:29:43 -0800
From:	Scott Feldman <scofeldm@...co.com>
To:	Simon Horman <horms@...ge.net.au>
CC:	<davem@...emloft.net>, <netdev@...r.kernel.org>
Subject: Re: [net-next PATCH 2/6] enic: Bug fix: try harder to fill Rx ring on
 skb allocation failures

On 12/19/09 5:15 PM, "Simon Horman" <horms@...ge.net.au> wrote:

> On Sat, Dec 19, 2009 at 12:39:03PM -0800, Scott Feldman wrote:
>>>> +  rq_work_done = rq_work_to_do;
>>> 
>>> Is it intentional for rq_work_done = rq_work_to_do to become the
>>> return value?
>> 
>> That was intentional.  If the replacement skb allocation fails, we're
>> returning like we did a full budget's worth of work so we stay scheduled and
>> hopefully the next polling pass we'll get the allocations.  Before this fix,
>> there is a corner case which isn't covered: if hw has used all descs and
>> gens an intr and we get into polling and the replacement alloc fails, then
>> Rx is hung.  Hw is desc starved and we're not going to get any more intrs:
>> game over.
> 
> Ok, understood. Though doesn't this fix just narrow the scope for that
> failure? It seems that it could still occur in a pathological case.

Oh!  The intention was to fix it absolutely.  Please expand on the
pathological case your thinking about.  We need this 100% solved, but now
you've got me worried...  ;)

-scott

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