Dequeue first or check the xmit_lock first?

[multisyncfe991]

Hello,

I read the Linux packet xmit function dev_queue_xmit in dev.c. The code 
works as follows:
1. enqueue a packet to the dsic queue
2. dequeue a packet
3. try to accquire xmi_lock, if available, then pass the packet to the 
driver
   otherwise, requeue the packet and let softirq to handle packet 
transmitting

My question is:
why not check the lock first? if the lock is available, then do dequeue. 
Thus we can
save unnecessary requeue operation.

Any idea about this?

Thanks,

Liang
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