Re: [patch 7/11] net: Use bigrefs for net_device.refcount

[Ravikiran G Thirumalai <kiran@scalex86.org>]

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