netdev - Re: [PATCH 3/4] sfc: resolve tx multiqueue bug

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Message-Id: <20080722.140023.127726788.davem@davemloft.net>
Date:	Tue, 22 Jul 2008 14:00:23 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	bhutchings@...arflare.com
Cc:	jgarzik@...ox.com, netdev@...r.kernel.org,
	linux-net-drivers@...arflare.com
Subject: Re: [PATCH 3/4] sfc: resolve tx multiqueue bug

From: Ben Hutchings <bhutchings@...arflare.com>
Date: Tue, 22 Jul 2008 19:41:19 +0100

> So long as a queue is only woken in response to TX completions, the current
> arrangement is fine.  However, sfc needs to tear down and restart hardware TX
> queues as part of some reconfiguration, self-test and recovery code, and I
> doubt it's the only such driver.

Mark the carrier off and packets will stop flowing to the driver.

Or, alternatively, take the necessary TX spinlocks around the
reconfiguration.

> I think the corresponding kernel queue must be stopped and then started when
> we do this (otherwise we could return NETDEV_TX_BUSY in hard_start_xmit, but
> I understand that to be deprecated).  So we must also wake the kernel queue
> if and only if it's considered active - but we don't know whether that's the
> case because deactivation is done asynchronously.

See above.
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