Pavel Emelyanov a écrit :
quoted text > I've found a much easier way to shrink the net_device structure
> rather that moving all the operations out of it. However, since
> the net_device may grow further, moving the operations into a
> separate place may look reasonable.
>
> The pahole tool showed, that there are a 124 and 80 bytes holes
> before the queue_lock and the _xmit_lock respectively. Moving most
> of the devices callbacks into the 2nd hole makes the sizeof of the
> structure be 1024 bytes.
>
>
On 32 bits platform and CONFIG_X86_L1_CACHE_SHIFT=7
I presume :)
Could you check if x86_64 machines with X86_L1_CACHE_SHIFT = 7 or 8
dont suffer from this patch ?
At first glance I would say it seems OK, but this net_device is really
touchy for SMP performance :)
quoted text > The hard_start_xmit callback is not moved to keep it in previous
> cacheline.
>
> I think it's OK to make such a reordering, since all these hooks
> are a) read-only and b) not called on fast paths, so their place
> within the structure looks not very important.
>
> Unfortunately diff makes the patch look like moving other fields,
> rater than the ops :)
>
> Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
>
> ---
> include/linux/netdevice.h | 47 +++++++++++++++++++++++----------------------
> 1 files changed, 24 insertions(+), 23 deletions(-)
>
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 8b17ed4..3397919 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -483,9 +483,6 @@ struct net_device
> struct list_head napi_list;
> #endif
>
> - /* The device initialization function. Called only once. */
> - int (*init)(struct net_device *dev);
> -
> /* ------- Fields preinitialized in Space.c finish here ------- */
>
> /* Net device features */
> @@ -641,27 +638,9 @@ struct net_device
> int watchdog_timeo; /* used by dev_watchdog() */
> struct timer_list watchdog_timer;
>
> -/*
> - * refcnt is a very hot point, so align it on SMP
> - */
> - /* Number of references to this device */
> - atomic_t refcnt ____cacheline_aligned_in_smp;
> -
> - /* delayed register/unregister */
> - struct list_head todo_list;
> - /* device index hash chain */
> - struct hlist_node index_hlist;
> -
> - struct net_device *link_watch_next;
> -
> - /* register/unregister state machine */
> - enum { NETREG_UNINITIALIZED=0,
> - NETREG_REGISTERED, /* completed register_netdevice */
> - NETREG_UNREGISTERING, /* called unregister_netdevice */
> - NETREG_UNREGISTERED, /* completed unregister todo */
> - NETREG_RELEASED, /* called free_netdev */
> - } reg_state;
>
> + /* The device initialization function. Called only once. */
> + int (*init)(struct net_device *dev);
> /* Called after device is detached from network. */
> void (*uninit)(struct net_device *dev);
> /* Called after last user reference disappears. */
> @@ -703,6 +682,28 @@ struct net_device
> unsigned short vid);
>
> int (*neigh_setup)(struct net_device *dev, struct neigh_parms *);
> +
> +/*
> + * refcnt is a very hot point, so align it on SMP
> + */
> + /* Number of references to this device */
> + atomic_t refcnt ____cacheline_aligned_in_smp;
> +
> + /* delayed register/unregister */
> + struct list_head todo_list;
> + /* device index hash chain */
> + struct hlist_node index_hlist;
> +
> + struct net_device *link_watch_next;
> +
> + /* register/unregister state machine */
> + enum { NETREG_UNINITIALIZED=0,
> + NETREG_REGISTERED, /* completed register_netdevice */
> + NETREG_UNREGISTERING, /* called unregister_netdevice */
> + NETREG_UNREGISTERED, /* completed unregister todo */
> + NETREG_RELEASED, /* called free_netdev */
> + } reg_state;
> +
> #ifdef CONFIG_NETPOLL
> struct netpoll_info *npinfo;
> #endif
>
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