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Date: Fri, 1 Apr 2022 14:50:08 -1000
From: Stephen Hemminger <stephen@networkplumber.org>
To: Mattias =?UTF-8?B?UsO2bm5ibG9t?= <mattias.ronnblom@ericsson.com>
Cc: <dev@dpdk.org>, Thomas Monjalon <thomas@monjalon.net>, David Marchand
<david.marchand@redhat.com>, <onar.olsen@ericsson.com>,
<Honnappa.Nagarahalli@arm.com>, <nd@arm.com>,
<konstantin.ananyev@intel.com>, <mb@smartsharesystems.com>, "Ola Liljedahl"
<ola.liljedahl@arm.com>
Subject: Re: [PATCH v2] eal: add seqlock
Message-ID: <20220401145008.25e1c9f5@shemminger-XPS-13-9360>
In-Reply-To: <20220330142602.108061-1-mattias.ronnblom@ericsson.com>
References: <98CBD80474FA8B44BF855DF32C47DC35D86F84@smartserver.smartshare.dk>
<20220330142602.108061-1-mattias.ronnblom@ericsson.com>
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Errors-To: dev-bounces@dpdk.org
On Wed, 30 Mar 2022 16:26:02 +0200
Mattias R=C3=B6nnblom <mattias.ronnblom@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 =3D 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.