[PATCH v2] eal: add seqlock

[Stephen Hemminger]

On Wed, 30 Mar 2022 16:26:02 +0200
Mattias Rönnblom <mattias.ronnblom at ericsson.com> wrote:

> +	__atomic_store_n(&seqlock->sn, sn, __ATOMIC_RELAXED);
> +
> +	/* __ATOMIC_RELEASE to prevent stores after (in program
> order)
> +	 * from happening before the sn store.
> +	 */
> +	rte_atomic_thread_fence(__ATOMIC_RELEASE);

Couldn't atomic store with __ATOMIC_RELEASE do same thing?

> +static inline void
> +rte_seqlock_write_end(rte_seqlock_t *seqlock)
> +{
> +	uint32_t sn;
> +
> +	sn = seqlock->sn + 1;
> +
> +	/* synchronizes-with the load acquire in rte_seqlock_begin()
> */
> +	__atomic_store_n(&seqlock->sn, sn, __ATOMIC_RELEASE);
> +
> +	rte_spinlock_unlock(&seqlock->lock);

Atomic store is not necessary here, the atomic operation in
spinlock_unlock wil assure theat the seqeuence number update is
ordered correctly.