netdev - Re: pktgen and spin_lock

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Message-ID: <4ADE2C00.8030900@candelatech.com>
Date:	Tue, 20 Oct 2009 14:30:40 -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

On 10/20/2009 02:22 PM, Eric Dumazet wrote:

> Problem is skb->queue_mapping has different meaning if skb is directly given to a real device ->  start_xmit()
>
> ( In this case skb->queue_mapping should be between [O ... real_num_tx_queues-1])
>
> But if it goes through dev_queue_xmit(), it should be set between [1 .. real_num_tx_queues], because
> dev_pick_tx() will decrement skb->queue_mapping
>
> In fact skb->queue_mapping only works for forwarded packets, not locally generated ones.
>
> I am too tired to cook a fix at this moment, sorry :(

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).

Thanks,
Ben

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

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