Re: [dpdk-dev] [PATCH v3 8/8] test/rcu: use compiler atomics for data sync

[Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>]

On 7/20/21 6:51 AM, Joyce Kong wrote:
> Covert rte_atomic usages to compiler atomic built-ins in
> rcu_perf testcases.
> 
> Signed-off-by: Joyce Kong <joyce.kong@arm.com>
> Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> Acked-by: Stephen Hemminger <stephen@networkplumber.org>
> ---
>   app/test/test_rcu_qsbr_perf.c | 98 +++++++++++++++++------------------
>   1 file changed, 49 insertions(+), 49 deletions(-)
> 
> diff --git a/app/test/test_rcu_qsbr_perf.c b/app/test/test_rcu_qsbr_perf.c
> index 3017e71120..cf7b158d22 100644
> --- a/app/test/test_rcu_qsbr_perf.c
> +++ b/app/test/test_rcu_qsbr_perf.c
> @@ -30,8 +30,8 @@ static volatile uint32_t thr_id;
>   static struct rte_rcu_qsbr *t[RTE_MAX_LCORE];
>   static struct rte_hash *h;
>   static char hash_name[8];
> -static rte_atomic64_t updates, checks;
> -static rte_atomic64_t update_cycles, check_cycles;
> +static uint64_t updates, checks;
> +static uint64_t update_cycles, check_cycles;
>   
>   /* Scale down results to 1000 operations to support lower
>    * granularity clocks.
> @@ -81,8 +81,8 @@ test_rcu_qsbr_reader_perf(void *arg)
>   	}
>   
>   	cycles = rte_rdtsc_precise() - begin;
> -	rte_atomic64_add(&update_cycles, cycles);
> -	rte_atomic64_add(&updates, loop_cnt);
> +	__atomic_fetch_add(&update_cycles, cycles, __ATOMIC_RELAXED);
> +	__atomic_fetch_add(&updates, loop_cnt, __ATOMIC_RELAXED);

Shouldn't __atomic_add_fetch() be used instead since it pseudo-code is
a bit simpler. What is the best option if return value is not actually
used?