On Tue, Sep 13, 2005 at 08:27:52PM +0200, Eric Dumazet wrote:
> Ravikiran G Thirumalai a écrit :
>
> Hum...
>
> Did you tried to place refcnt/netdev_refcnt in a separate cache line than
> queue_lock ? I got good results too...
>
> > /* device queue lock */
> > spinlock_t queue_lock;
> > /* Number of references to this device */
> > - atomic_t refcnt;
> > + struct bigref netdev_refcnt ____cacheline_aligned_in_smp ;
> > /* delayed register/unregister */
> > struct list_head todo_list;
> > /* device name hash chain */
>
> Every time a cpu take the queue_lock spinlock, it exclusively gets one
> cache line. If another cpu try to access netdev_refcnt, it has to grab this
> cache line (even if properely per_cpu designed, there is still one shared
> field). In fact the whole struct net_device should be re-ordered for
> SMP/NUMA performance.
I agree. Maybe placing the queue_lock in a different cacheline is the
right approach?
Thanks,
Kiran
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