netdev - Re: [PATCH net-next 3/3] sunvnet: Schedule maybe_tx_wakeup as a tasklet from ldc

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Message-Id: <20140812.222941.2255442432293393813.davem@davemloft.net>
Date:	Tue, 12 Aug 2014 22:29:41 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	Raghuram.Kothakota@...cle.com
Cc:	sowmini.varadhan@...cle.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 3/3] sunvnet: Schedule maybe_tx_wakeup as a
 tasklet from ldc_rx path

From: Raghuram Kothakota <Raghuram.Kothakota@...cle.com>
Date: Tue, 12 Aug 2014 22:14:09 -0700

> On Aug 12, 2014, at 9:31 PM, David Miller <davem@...emloft.net> wrote:
> 
>> From: Raghuram Kothakota <Raghuram.Kothakota@...cle.com>
>> Date: Tue, 12 Aug 2014 21:26:28 -0700
>> 
>>> One important point to keep in mind that packets to different peers shouldn't
>>> be blocked by one blocked peer. Any flow controlling or dropping of the packets
>>> needs to be done on a per-port basis.
>> 
>> Until we use a big hammer and reset the LDC channel of that peer, we
>> _absolutely_ should not reorder traffic and send to non-stuck peers.
> 
> The packet ordering requirement applies only for packets destined to
> a specific destination. The packets to different destinations can flow
> as long as they do not cause ordering issues. In case of sunvnet, 
> each peer except the switch-port would be for a specific destination,
> so sending packets to other ports would not result in re-ordering of the packets.
> 
> Even if the peer to peer LDC is the one that is blocked then disconnecting
> that LDC channel and sending the packets via switch-port would not be
> expected to change the order of the packet as the LDC reset is expect
> to drop all packets in the ring so far.  

Ok, that makes sense.

So the question is how to manage this on the driver side, and the most
natural way I see do this would be to use multiple TX netdev queues
and a custom netdev_ops->ndo_select_queue() method which selects the
queue based upon the peer that would be selected.
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