netdev - Re: pktgen and spin_lock

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Message-ID: <4ADE7A63.4090404@candelatech.com>
Date:	Tue, 20 Oct 2009 20:05:07 -0700
From:	Ben Greear <greearb@...delatech.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	NetDev <netdev@...r.kernel.org>, robert@...julf.net,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: pktgen and spin_lock_bh in xmit path

Ben Greear wrote:
> On 10/20/2009 02:57 PM, Eric Dumazet wrote:
>> Ben Greear a écrit :
>>> That's definitely a nasty little issue.  Using skb_set_queue_mapping
>>> in pktgen makes it run for me, but may just be getting lucky with the
>>> mac-vlan interfaces which will do the dev_queue_xmit (but, I don't 
>>> so much
>>> care exactly what queue is used as long as things don't crash and the
>>> link doesn't reset).
>>>
>>> Don't worry about a quick patch on my account.  I seem to have it 
>>> working
>>> to at least some degree (no funny crashes, no link watchdog timeouts).
>>>
>>
>> Could you try following patch ?
>>
>> This makes queue_mapping invariant if set in range [0 ... 
>> real_num_tx_queues-1]
>
> Yes, that runs w/out causing link resets and without crashes (just 
> tested it for
> a few minutes).
>
> Interestingly, the pkts sent by pktgen on the mac-vlans end up in
> tx-queues that match processor ID, even though I'm on .31 where mac-vlans
> have only one tx-queue and pktgen is setting the queue to 0 in the skb
> (per your previous patch).
Ok, this is because ixgbe implements the ndo_select_queue, which is 
called from
dev_pick_tx.

So, as far as I can tell, as long as you are using ixgbe with 82559, it 
doesn't matter what you set
for the queue-map in the skb..it's always over-written.

I don't know if this is a bug or a feature, but it explains the behavior 
with tx and rx queues
that I saw when using pktgen on mac-vlans...

Thanks,
Ben

-- 
Ben Greear <greearb@...delatech.com> 
Candela Technologies Inc  http://www.candelatech.com


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