On Mon, 17 Jun 2013, Kent Overstreet wrote:
> +static inline unsigned alloc_local_tag(struct percpu_ida *pool,
> + struct percpu_ida_cpu *tags)
> +{
> + int tag = -ENOSPC;
> +
> + spin_lock(&tags->lock);
> + if (tags->nr_free)
> + tag = tags->freelist[--tags->nr_free];
> + spin_unlock(&tags->lock);
> +
> + return tag;
> +}
This could be made much faster by avoiding real atomics (coming with
spinlocks) and using per cpu atomics instead. Slub f.e. uses a single
linked per cpu list managed via this_cpu_cmpxchg.
In order to avoid locking completely the state of the percpu tag list must
fit into one word that can be handled via the local cmpxchg (or two with
the cmpxchg_double). May require some changes to the data structure.
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