netdev - RE: [PATCH net-next] bnx2x: avoid soft lockup in bnx2x

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Date:	Tue, 8 Dec 2015 17:02:44 +0000
From:	Yuval Mintz <Yuval.Mintz@...gic.com>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>
CC:	netdev <netdev@...r.kernel.org>,
	Ariel Elior <Ariel.Elior@...gic.com>,
	Willem de Bruijn <willemb@...gle.com>
Subject: RE: [PATCH net-next] bnx2x: avoid soft lockup in bnx2x_poll()

> Under heavy TX load, bnx2x_poll() can loop forever and trigger soft lockup bugs.
> 
> A napi poll handler must yield after one TX completion round, risk of livelock is
> too high otherwise.
> 
> Bug is very easy to trigger using a debug build, and udp flood, because of added
> cpu cycles in TX completion, and we do not receive enough packets to break the
> loop.

Eric - I understand what you're doing and it looks fine [to me, at least].
Out of curiosity, do you know whether removing the loop damages any
other flow, i.e., by slowing transmitter as transmission rings gets filled
completely between consecutive NAPI runs?