netdev - sunvnet NAPIfication

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Message-ID: <20141015140500.GA11183@oracle.com>
Date:	Wed, 15 Oct 2014 10:05:00 -0400
From:	Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org
Subject: sunvnet NAPIfication


I have the NAPIfication-of-sunvnet patch-set ready for 
code review. AFAIK net-next is not currently open
for new features this week, but does it make sense for
me to go ahead and send the patch-set to the list (I'm sure
it will take some time to review) or will that just create
confusion to the netdev maintainers?

--Sowmini

Previously discussed:

> >> For example, you can now move everything into software IRQ context,
> >> just disable the VIO interrupt and unconditionally go into NAPI
> >> context from the VIO event.
> >> No more irqsave/irqrestore.
> >> Then the TX path even can run mostly lockless, it just needs
> >> to hold the VIO lock for a minute period of time.  The caller
> >> holds the xmit_lock of the network device to prevent re-entry
> >> into the ->ndo_start_xmit() path.
> 
> I think you should be able to get rid of all of the in-driver
> locking in the fast paths.
> 
> NAPI ->poll() is non-reentrant, so all RX processing occurs
> strictly in a serialized environment.
> 
> Once you do TX reclaim in NAPI context, then all you have to do is
> take the generic netdev TX queue lock during the evaluation of whether
> to wakeup the TX queue or not.  Worst case you need to hold the
> TX netdev queue lock across the whole TX reclaim operation.
> 
> The VIO lock really ought to be entirely superfluous in the data
> paths.
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