netdev - [PATCH net-next 0/2] sunvnet: Packet processing in non-interrupt context

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Message-ID: <20141001202454.GO17706@oracle.com>
Date:	Wed, 1 Oct 2014 16:24:54 -0400
From:	Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:	davem@...emloft.net, raghuram.kothakota@...cle.com,
	sowmini.varadhan@...cle.com, david.stevens@...cle.com
Cc:	netdev@...r.kernel.org
Subject: [PATCH net-next 0/2] sunvnet: Packet processing in non-interrupt
 context

The existing sunvnet implementation does all the packet interception
in LDC interrupt context. Patch 1 of this series moves the data
processing to a bottom-half handler.

Some context for the reasons for choosing a BH handler over NAPI:
   A NAPI (or simple tasklet) based implementation provides softirq
   context, which allows the driver to safely invoke netif_receive_skb()
   to deliver the packet to the IP stack. But in the case of sunvnet,
   we are already receiving multiple packets for a single ldc_rx
   interrupt, so the budget-based softirq-vs-polling infra does not
   provide a significant optimization. Rather, it can get in the way,
   if we constrain the vnet-rx path to a poorly chosen budget, and force
   ourselves to send a STOPPED/START ldc exchange needlessly.

   A BH Rx handler is a simpler way to  avoid the weaknesses of processing
   packets in LDC interrupt context, and also provides Rx load-spreading
   across multiple CPUs.

Note that PATCH 1 is dependant on the functions added as part of the
sparc-next commit "sparc64: Add vio_set_intr() to enable/disable Rx interrupts"
(Cf: http://www.spinics.net/lists/sparclinux/msg12647.html)

PATCH 2 of this series fixes a race-condition between vnet_port_remove()
and vnet_start_xmit().

changes since v1 to Patch 2: revert switch_port caching in struct vnet

Sowmini Varadhan (2):
  Process Rx data packets in a BH handler
  vnet_start_xmit() must hold a refcnt on port.

 drivers/net/ethernet/sun/sunvnet.c | 187 +++++++++++++++++++++++++++----------
 drivers/net/ethernet/sun/sunvnet.h |  12 ++-
 2 files changed, 146 insertions(+), 53 deletions(-)

-- 
1.8.4.2

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