The attached patch is based on tg3.c as found in 2.4.20-rc3 or the 
latest Linus 2.5.x kernel, and originates from two motivations:

* When net drivers move TX completion from interrupt to dev->poll(), 
this allows the rethinking of some traditional locking, namely 
eliminating a lock in dev->start_xmit() that most drivers implement 
these days.

* Specific to the tg3 implementation, spin-lock-irq is held during NIC 
hardware halt and re-initialization (and a few other operations).  In 
general a goal is to change this; the driver may wind up holding 
interrupts disabled for longer than prudence dictates.  The attached 
patch does not address this issue directly, but it does begin to lay the 
groundwork for my upcoming solution :)

I mention "NAPI" in the subject because other NAPI drivers may wish to 
re-examine their locking as well, and this patch could serve as a basis 
for discussion.


Overall, I believe the attached patch (after testing/debugging/review) 
will make the tg3 driver faster due to less locking in dev->start_xmit, 
and more friendly system interaction because interrupts are being 
disabled->enabled less frequently by this driver.


Here is a function-by-function description of changes, which gives one a 
better idea of the locking changes that may be a found in a driver:

all functions:  s/spin_lock_irq/spin_lock_irqsave/ to be more 
conservative and "obviously safe"

all functions:  locking ordering now reversed:  dev->xmit_lock obtained 
before tp->lock.

tg3_set_power_state: Do not call tg3_halt(), the one case where this 
code path is hit, the caller has already called tg3_halt()

tg3_poll: hold dev->xmit_lock when checking for TX work, and running TX 
completion cycle.  tp->tx_lock GC'd.

tg3_tx_timeout: net stack already holds dev->xmit_lock.  tx_lock GC'd.

tg3_{4gbug}_start_xmit: net stack already holds dev->xmit_lock, no other 
locks needed (whee!), so:  tp->lock GC'd.

tg3_change_mtu: get dev->xmit_lock instead of tp->tx_lock. wrap locking 
in netif_start_queue ... netif_wake_queue.

tg3_timer: get xmit_lock instead of tx_lock.  wrap NIC reset in 
netif_start_queue ... netif_wake_queue.

tg3_open: no need for tx locking, just move netif_start_queue down to 
the bottom of the function.

tg3_close: s/tp->tx_lock/dev->xmit_lock/

tg3_get_regs: likewise

tg3_ethtool_ioctl: likewise, plus netif_{start,wake}_queue wrap around 
NIC reset

tg3_vlan_rx_register: remove TX lock

tg3_vlan_rx_kill_vid: remove TX lock

tg3_suspend: s/tp->tx_lock/dev->xmit_lock/, netif_{start,wake}_queue wrap

tg3_resume: likewise

Th-th-th-th-that's all, folks!

Questions/comments/flames requested.