netdev - Re: pktgen and spin_lock

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Message-ID: <4ADE9D07.2020506@candelatech.com>
Date:	Tue, 20 Oct 2009 22:32:55 -0700
From:	Ben Greear <greearb@...delatech.com>
To:	Krishna Kumar2 <krkumar2@...ibm.com>
CC:	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	NetDev <netdev@...r.kernel.org>, netdev-owner@...r.kernel.org,
	robert@...julf.net
Subject: Re: pktgen and spin_lock_bh in xmit path

Krishna Kumar2 wrote:
> Ben Greear <greearb@...delatech.com>  wrote on 10/21/2009 02:40:13 AM:
>
> Coming back a bit to this post:
>
>   
>>> -   queue_map = skb_get_queue_mapping(pkt_dev->skb);
>>> +   queue_map = pkt_dev->cur_queue_map;
>>> +   /*
>>> +    * tells skb_tx_hash() to use this tx queue.
>>> +    * We should reset skb->mapping before each xmit() because
>>> +    * xmit() might change it.
>>> +    */
>>> +   skb_record_rx_queue(pkt_dev->skb, queue_map);
>>>      txq = netdev_get_tx_queue(odev, queue_map);
>>>       
>> I think that must be wrong.  The record_rx_queue sets it to queue_map + 1,
>>     
>> but the hard-start-xmit method (in ixgbe/ixgbe_main.c, at least), takes the
>> skb->queue_map and uses it as an index with no subtraction.
>>     
>
> But that should work fine. record_rx_q sets queue_mapping to +1,
> but skb_tx_hash calls skb_get_rx_queue, which does a -1 on this
> value, and updates that value into queue_mapping. Hence it will
> not cross the txq boundary. Drivers can use the queue_map value
> directly without requiring to subtract.
>   
When using pktgen on real physical hardware, there is none of the 
skb_tx_hash or dev_queue_xmit
logic called, just the hard-start-xmit.  That is why it fails to update 
the proper queue with
his first patch. 

On virtual devices like mac-vlans, the logic probably worked ok since it 
goes
through dev_queue_xmit.

Thanks,
Ben

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


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