netdev - Re: [PATCH net] bonding: fix arp monitoring with vlan slaves

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Date:	Fri, 02 Aug 2013 17:03:43 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Nikolay Aleksandrov <nikolay@...hat.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	andy@...yhouse.net, fubar@...ibm.com
Subject: Re: [PATCH net] bonding: fix arp monitoring with vlan slaves

On Sat, 2013-08-03 at 01:29 +0200, Nikolay Aleksandrov wrote:

> I knew it was because of the LLTX, but I was wondering about the possible
> reasons for the xmit_lock_owner check.
> So basically the arp monitoring (or any dev_trans_start code) won't work
> with LLTX devices because they don't get their trans_start updated (not the
> txq trans_start nor the dev->trans_start), is this correct ?

Nope : LLTX devices are supposed to update their own dev->trans_start
I added for these case a special comment as in :

drivers/net/ethernet/atheros/atl1e/atl1e_main.c:1883:   netdev->trans_start = jiffies; /* NETIF_F_LLTX driver :( */

trans_start is a txq property, and vlan devices have a single txq.

Updating the vlandev->trans_start or the vlantxq->trans_start would be a
performance killer on MQ ethernet.

And frankly, as this trans_start is really seldom queried, it makes no
sense to set it on fast path on the vlan device, if its properly done on
the real device anyway.

> But what if the txqs get bound to a particular CPU, then the txq
> trans_start is okay to be updated I suppose.

Not sure what you are saying. vlan xmit can be called from any cpus.

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