Le lundi 18 octobre 2010 Ã 10:24 -0500, Christoph Lameter a Ãcrit :
> On Sat, 16 Oct 2010, Eric Dumazet wrote:
>
> > I based following patch against linux-2.6, I dont know if previous
> > Christoph patch is in a git tree. I'll respin it eventually.
>
> The prior patch was accepted by Andrew.
>
> > + * - It is preempt safe, but not IRQ safe (on UP)
>
> The IRQ safeness depends on the arch. this_cpu_add() in general only
> guarantees safety against preemption. It so happens that the x86
> implementation is irq safe as well.
>
> The IRQ safety for UP is therefore not an issue if you use this_cpu_add().
>
Nope, on UP, we dont use a per_cpu field, just a "s64 count".
struct percpu_counter {
s64 count;
};
> If you want to guarantee irqsafeness then use irqsafe_cpu_add() instead.
> It generates the same code on x86 for SMP but takes care of the UP issues.
>
> > +static inline void percpu_counter_add_fast(struct percpu_counter *fbc, long amount)
> > +{
> > + this_cpu_add(*fbc->counters, amount);
> > +}
>
> What happens in case of counter overflow?
>
Nothing special, as I stated the usuable width of such counters would be
restricted to a long, not an s64.
It should be enough to count "number of inodes, of sockets, ..."
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
