Forcedeth Improvements

Jeff Garzik posted a series of five patches [1] for the forcedeth driver which he described as, "several proposed updates for testing". Forcedeth is a GPL'd driver for the Ethernet interface of the NVIDIA nForce chipset, originally merged into the 2.4.26 and 2.6.5 Linux kernels. Jeff noted two main goals for the patches:

"1) move the driver towards a more sane, simple, easy to verify locking setup -- irq handler would often acquire/release the lock twice for each interrupt.

"2) to eliminate a rarely used, apparently fragile locking scheme that includes heavy use of disable_irq(). this tool is most often employed during NIC reset/reconfiguration, so satisfying this goal implies changing the way NIC reset and config are accomplished."

Jeff explained that he was looking to get the changes tested, "these are intended for feedback and testing, NOT for merging." He went on to explain that one of the changes included two independent napi_structs, one for receiving and one transmitting, "I feel TX NAPI is a useful tool, because it provides an independent TX process control point and system load feedback point. Thus I felt this was slightly superior to tasklets. But who knows if this is a good idea? :) I am interested in feedback and criticism on this issue."

From: Jeff Garzik <jeff@...>
Subject: [PATCH 0/5] forcedeth: several proposed updates for testing
 [1]Date: Oct 6, 11:12 am 2007

The 'fe-lock' branch of
git://git.kernel.org/pub/scm/linux/kernel/git/jgarzik/netdev-2.6.git fe-lock

contains the following changes that I would like to get tested:

      [netdrvr] forcedeth: make NAPI unconditional
      [netdrvr] forcedeth: interrupt handling cleanup
      [netdrvr] forcedeth: process TX completions using NAPI
      [netdrvr] forcedeth: internal simplification and cleanups
      [netdrvr] forcedeth: timer overhaul

These are intended for feedback and testing, NOT for merging.

The goals of these changes are:
* move the driver towards a more sane, simple, easy to verify locking
  setup -- irq handler would often acquire/release the lock twice
  for each interrupt -- and hopefully

* to eliminate a rarely used, apparently fragile locking scheme that
  includes heavy use of disable_irq().  this tool is most often employed
  during NIC reset/reconfiguration, so satisfying this goal implies
  changing the way NIC reset and config are accomplished.

Miscellaneous notes:
* using the new napi_struct stuff in net-2.6.24, the TX completion
  process has been moved to a -separate- NAPI polling channel.  thus
  there are now two napi_structs, one for RX and one for TX, independent
  of each other.

* I feel TX NAPI is a useful tool, because it provides an independent TX
  process control point and system load feedback point.
  Thus I felt this was slightly superior to tasklets.

* But who knows if this is a good idea?  :)  I am interested in
  feedback and criticism on this issue.

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Forcedeth Improvements

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