netdev - Re: [PATCH net-next 2/2] sunvnet: vnet_start

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Date:	Wed, 1 Oct 2014 20:36:38 -0700
From:	Raghuram Kothakota <Raghuram.Kothakota@...cle.com>
To:	David Miller <davem@...emloft.net>
Cc:	david.stevens@...cle.com, sowmini.varadhan@...cle.com,
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next 2/2] sunvnet: vnet_start_xmit() must hold a refcnt on port.


On Oct 1, 2014, at 12:52 PM, David Miller <davem@...emloft.net> wrote:

> From: David L Stevens <david.stevens@...cle.com>
> Date: Wed, 01 Oct 2014 15:31:49 -0400
> 
>> 
>> 
>> On 10/01/2014 03:23 PM, Sowmini Varadhan wrote:
>>> On (10/01/14 15:06), David L Stevens wrote:
>>>> 
>>>> This "vp->switch_port" addition doesn't appear to be related to the port refcnt
>>>> change, and doesn't allow for multiple switch ports.
>>> 
>>> The switch_port is the connection to Dom0. Do you envision us having more than
>>> one switch_port? How?
>> 
>> While Dom0 might only create one port with the "switch" flag, the flag just means
>> "I can reach anybody" and is not inherently unique. I don't think an attached
>> VM should assume there is always only one; it prevents multipath load balancing
>> kinds of things in the future.
>> 
>> Also, there is the broader point that this sort of change should be a separate patch.
>> It isn't required for fixing the dangling reference -- it is an independent change.
> 
> Multiple switch ports are absolutely allowed by the protocol spec and can
> provide the suggested facilities David mentioned, don't prevent them from
> being used.

In reality, introducing multiple switch-ports will need Guest driver change
as well. The existing sunvnet driver will not automatically utilize all switch-ports
and requires changes. When we add the full support to use multiple switch-ports,
I am sure we can change the current optimization for switch-port lookup with
a different method probably with another optimized method than what it is today.

-Raghuram--
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