Jiri Pirko a écrit : > Sat, Apr 18, 2009 at 09:35:32AM CEST, dada1@xxxxxxxxxxxxx wrote: >> Jiri Pirko a écrit : >>> Fri, Apr 17, 2009 at 05:33:15PM CEST, shemminger@xxxxxxxxxx wrote: >>> >>> <snip> >>> >>>>> +struct netdev_hw_addr { >>>>> + struct list_head list; >>>>> + unsigned char addr[MAX_ADDR_LEN]; >>>>> + int refcount; >>>>> + struct rcu_head rcu_head; >>>>> +}; >>>> Minor nit, the ordering of elements cause holes that might not be >>>> needed. >>> Agree that ordering might be done better. Will do. >>>> Space saving? is rcu_head needed or would using synchronize_net >>>> make code cleaner and save space. >>>> >>> Well I originaly had this done by synchronize_rcu(). Eric argued that it might >>> cause especially __hw_addr_del_multiple_ii() to run long and suggested to use >>> call_rcu() instead. I plan to switch this to kfree_rcu() (or whatever it's >>> called) once it hits the tree. >>> >> Yes, and dont forget we wont save space, as we allocate a full >> cache line to hold a 'struct netdev_hw_addr', since we dont want this >> critical and read_mostly object polluted by a hot spot elsewhere in kernel... >> >> Considering this, letting 'rcu_head' at the end of structure, even if we >> have an eventual hole on 64 bit arches is not really a problem, and IMHO >> the best thing to do, as rcu_head is only used at dismantle time. > > I will order the struct better, there are archs with small cache line size where > it makes sense. How exactly ? If you consider a 32bit arch with 16 or 32 bytes cache line, sizeof(struct_list_dead) is 8 sizeof(addr) = 32 (but we really use 6 bytes for ethernet) struct netdev_hw_addr { unsigned char addr[MAX_ADDR_LEN]; struct list_head list; int refcount; struct rcu_head rcu_head; }; would cost more at lookup time, since we would use two cache lines struct netdev_hw_addr { struct list_head list; unsigned char addr[MAX_ADDR_LEN]; int refcount; struct rcu_head rcu_head; }; Is nicer, because at least 8 bytes of addr share the same cache line than list. So direct dev->dev_addr would be fast (for devices with one address), and is_etherdev_addr() would still use one cache line per item. _______________________________________________ Bridge mailing list Bridge@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/bridge