Re: [PATCH] netfilter: save the hash of the tuple in the originaldirection for latter use

[Changli Gao]

On Tue, Aug 17, 2010 at 4:30 PM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
>
> Three variables ?
>
> static atomic_t rnd __read_mostly;
>
> if (unlikely(!atomic_read(&rnd))) {
>        unsigned int val;
>
>        get_random_bytes(&val, sizeof(val));
>        if (!val)
>                val = 1;
>        atomic_cmpxchg(&rnd, 0, val);
> }
>


Good idea. However, atomic_t is a volatile variable, and it prevent
ILP. I think maybe it hurts the likely case. cmpxchg() is an atomic
operations, so is the bellow code better?

 static unsigned long rnd __read_mostly;

 if (unlikely(!rnd)) {
        unsigned long val;

        get_random_bytes(&val, sizeof(val));
        if (!val)
                val = 1;
        cmpxchg(&rnd, 0, val);
 }

Thanks.

-- 
Regards,
Changli Gao(xiaosuo@xxxxxxxxx)
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