netdev - Re: [PATCH RFC]: napi

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Message-ID: <ada1wesy2eh.fsf@cisco.com>
Date:	Sat, 28 Jul 2007 08:27:18 -0700
From:	Roland Dreier <rdreier@...co.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, shemminger@...ux-foundation.org,
	jgarzik@...ox.com, hadi@...erus.ca, rusty@...tcorp.com.au
Subject: Re: [PATCH RFC]: napi_struct V4

 > Most drivers are in good shape, although some still have very
 > questionable netif_rx_complete() handling, in that racy area that
 > Rusty and myself were discussing today.
 > 
 > My inclination is to wrap those sequences around with an IRQ
 > safe spinlock to fix the race provably, and then if driver
 > authors want to optimize that away with techniques like those
 > that tg3, bnx2, sky2, skge et al. use, that's fine but can
 > be done later.

Ouch... that extra lock seems pretty expensive.  Also I'm having a
hard time understanding how the techniques you're alluding to apply to
devices that may miss events when enabling interrupts; the drivers you
mention all seem to be for devices that didn't have the race and
didn't use netif_rx_reschedule() in the old NAPI world.  Can you
provide a little more detail on how the lock could be optimized away?

Thanks,
  Roland
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