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* Is netif_tx_lock() SMP PREEMPT safe?
@ 2008-02-15 15:25 Marin Mitov
  2008-02-15 16:01 ` Eric Dumazet
  0 siblings, 1 reply; 2+ messages in thread
From: Marin Mitov @ 2008-02-15 15:25 UTC (permalink / raw)
  To: linux-kernel

Hi all,

As in: include/linux/netdevice.h (kernel-2.6.24.2) one finds:

static inline void __netif_tx_lock(struct net_device *dev, int cpu)
{
        spin_lock(&dev->_xmit_lock);
        dev->xmit_lock_owner = cpu;
}

static inline void netif_tx_lock(struct net_device *dev)
{
        __netif_tx_lock(dev, smp_processor_id());
}

Does netif_tx_lock(struct net_device *dev) expands into:

cpu = smp_processor_id(); 
<preempt & shift to another cpu (bogus)>
spin_lock(&dev->_xmit_lock);
dev->xmit_lock_owner = cpu; /* cpu is not the lock owner */

Or to:

spin_lock(&dev->_xmit_lock);
dev->xmit_lock_owner = smp_processor_id();

which is correct?

Thanks in advance for your answer.

Regards

Marin Mitov



^ permalink raw reply	[flat|nested] 2+ messages in thread

* Re: Is netif_tx_lock() SMP PREEMPT safe?
  2008-02-15 15:25 Is netif_tx_lock() SMP PREEMPT safe? Marin Mitov
@ 2008-02-15 16:01 ` Eric Dumazet
  0 siblings, 0 replies; 2+ messages in thread
From: Eric Dumazet @ 2008-02-15 16:01 UTC (permalink / raw)
  To: Marin Mitov; +Cc: linux-kernel, netdev

Marin Mitov a écrit :
> Hi all,
>
> As in: include/linux/netdevice.h (kernel-2.6.24.2) one finds:
>
> static inline void __netif_tx_lock(struct net_device *dev, int cpu)
> {
>         spin_lock(&dev->_xmit_lock);
>         dev->xmit_lock_owner = cpu;
> }
>
> static inline void netif_tx_lock(struct net_device *dev)
> {
>         __netif_tx_lock(dev, smp_processor_id());
> }
>
> Does netif_tx_lock(struct net_device *dev) expands into:
>
> cpu = smp_processor_id(); 
> <preempt & shift to another cpu (bogus)>
> spin_lock(&dev->_xmit_lock);
> dev->xmit_lock_owner = cpu; /* cpu is not the lock owner */
>
> Or to:
>
> spin_lock(&dev->_xmit_lock);
> dev->xmit_lock_owner = smp_processor_id();
>
> which is correct?
>
>   
Hi Marin

This expands to the first version, but netif_tx_lock() is allways called 
with preemption disabled.

(Or checks in smp_processor_id() would just trigger)


Eric
(Cced netdev for network related stuff)






^ permalink raw reply	[flat|nested] 2+ messages in thread

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