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Date: Wed, 11 Jul 2018 13:49:07 -0700
From: Stephen Hemminger <stephen@networkplumber.org>
To: Yipeng Wang <yipeng1.wang@intel.com>
Cc: pablo.de.lara.guarch@intel.com, dev@dpdk.org,
 bruce.richardson@intel.com, honnappa.nagarahalli@arm.com,
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Subject: Re: [dpdk-dev] [PATCH v5 5/8] hash: add read and write concurrency
 support
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On Tue, 10 Jul 2018 09:59:58 -0700
Yipeng Wang <yipeng1.wang@intel.com> wrote:

> +
> +static inline void
> +__hash_rw_reader_lock(const struct rte_hash *h)
> +{
> +	if (h->readwrite_concur_support && h->hw_trans_mem_support)
> +		rte_rwlock_read_lock_tm(h->readwrite_lock);
> +	else if (h->readwrite_concur_support)
> +		rte_rwlock_read_lock(h->readwrite_lock);
> +}
> +
> +static inline void
> +__hash_rw_writer_unlock(const struct rte_hash *h)
> +{
> +	if (h->multi_writer_support && h->hw_trans_mem_support)
> +		rte_rwlock_write_unlock_tm(h->readwrite_lock);
> +	else if (h->multi_writer_support)
> +		rte_rwlock_write_unlock(h->readwrite_lock);
> +}
> +
> +static inline void
> +__hash_rw_reader_unlock(const struct rte_hash *h)
> +{
> +	if (h->readwrite_concur_support && h->hw_trans_mem_support)
> +		rte_rwlock_read_unlock_tm(h->readwrite_lock);
> +	else if (h->readwrite_concur_support)
> +		rte_rwlock_read_unlock(h->readwrite_lock);
> +}
> +

For small windows, reader-writer locks are slower than a spin lock
because there are more cache bounces.