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

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Message-Id: <8BE2AE04-EF39-45A0-9AB4-15F5160C1449@oracle.com>
Date:	Tue, 12 Aug 2014 22:14:09 -0700
From:	Raghuram Kothakota <Raghuram.Kothakota@...cle.com>
To:	David Miller <davem@...emloft.net>
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

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.  

-Raghuram
> 
> A networking stack should avoid packet reordering in all cases when it
> has the ability to do so, and sending packets which came in later to
> unstuck peers when there are older packets still pending to the stuck
> peer violates that requirement.

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