On Thu, 30 Sep 2010 12:22:16 +0200 Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
> Le jeudi 30 septembre 2010 __ 01:14 -0700, Andrew Morton a __crit :
>
> > Perhaps
> >
> > WARN_ON_ONCE(preemptible());
> >
> > if we had a developer-only version of WARN_ON_ONCE, which we don't.
>
> Or just use a regular PER_CPU variable, even on !SMP, and get preempt
> safe implementation.
Good stuff.
> What do you think of following patch, on top of current linux-2.6 tree ?
>
> ...
>
> +static noinline unsigned int last_ino_get(void)
> +{
> + unsigned int *p = &get_cpu_var(last_ino);
> + unsigned int res = *p;
> +
> +#ifdef CONFIG_SMP
> + if (unlikely((res & (LAST_INO_BATCH - 1)) == 0)) {
> + static atomic_t shared_last_ino;
> + int next = atomic_add_return(LAST_INO_BATCH, &shared_last_ino);
> +
> + res = next - LAST_INO_BATCH;
> + }
> +#endif
> + *p = ++res;
> + put_cpu_var(last_ino);
> + return res;
> +}
Could eliminate `p' I guess, but that would involve using
__get_cpu_var() as an lval, which looks vile and might generate worse
code.
Readers of this code won't know why last_ino_get() was marked noinline.
It looks wrong, really.
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