Re: High contention on the sk_buff_head.lock

[Herbert Xu]

David Miller <davem@xxxxxxxxxxxxx> wrote:
> From: Eric Dumazet <dada1@xxxxxxxxxxxxx>
> Date: Mon, 23 Mar 2009 09:32:39 +0100
> 
>> I dont understand, doesnt it defeat the ticket spinlock thing and fairness ?
>> 
>> Thread doing __qdisc_run() already owns the __QDISC_STATE_RUNNING bit.
> 
> Right.
> 
> Remember, the way this is designed is that if there is a busy
> cpu taking packets out of the queue and putting them into the
> device then other cpus will simply add to the queue and immediately
> return.  This effectively keeps the queue running there processing
> all the new work that other cpus are adding to the qdisc.
> 
> Those other cpus make these decisions by looking at that
> __QDISC_STATE_RUNNING bit, which the queue runner grabs before
> it does any work.

Come on guys, if this lock is a problem. go out and buy a proper
NIC that supports multiequeue TX!

Cheers,
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