[RFC] eal: add seqlock

[Stephen Hemminger]

On Fri, 25 Mar 2022 21:24:28 +0100
Mattias Rönnblom <mattias.ronnblom at ericsson.com> wrote:

> diff --git a/lib/eal/include/rte_seqlock.h b/lib/eal/include/rte_seqlock.h
> new file mode 100644
> index 0000000000..b975ca848a
> --- /dev/null
> +++ b/lib/eal/include/rte_seqlock.h
> @@ -0,0 +1,84 @@
> +/* SPDX-License-Identifier: BSD-3-Clause
> + * Copyright(c) 2022 Ericsson AB
> + */
> +
> +#ifndef _RTE_SEQLOCK_H_
> +#define _RTE_SEQLOCK_H_
> +
> +#include <stdbool.h>
> +#include <stdint.h>
> +
> +#include <rte_atomic.h>
> +#include <rte_branch_prediction.h>
> +#include <rte_spinlock.h>
> +
> +struct rte_seqlock {
> +	uint64_t sn;
> +	rte_spinlock_t lock;
> +};
> +
> +typedef struct rte_seqlock rte_seqlock_t;
> +


Add a reference to Wikipedia and/or Linux since not every DPDK
user maybe familar with this.

> +
> +	sn = seqlock->sn + 1;
> +
> +	__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);

Could this just be __atomic_fetch_add() with __ATOMIC_RELEASE?