Re: [dpdk-dev] [PATCH v2 6/6] test/ring: use relaxed barriers for ring stress test

["Ananyev, Konstantin" <konstantin.ananyev@intel.com>]

 
> wrk_cmd variable is used to signal the worker thread to start
> or stop the stress test loop. Relaxed barriers are used
> to achieve the same.
> 
> Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> Reviewed-by: Ola Liljedahl <ola.liljedahl@arm.com>
> Reviewed-by: Feifei Wang <feifei.wang@arm.com>
> ---
>  app/test/test_ring_stress_impl.h | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/app/test/test_ring_stress_impl.h b/app/test/test_ring_stress_impl.h
> index f9ca63b908..ee8293bb04 100644
> --- a/app/test/test_ring_stress_impl.h
> +++ b/app/test/test_ring_stress_impl.h
> @@ -22,7 +22,7 @@ enum {
>  	WRK_CMD_RUN,
>  };
> 
> -static volatile uint32_t wrk_cmd __rte_cache_aligned;
> +static volatile uint32_t wrk_cmd __rte_cache_aligned = WRK_CMD_STOP;

If we switch to using atomic load/store for 'wrk_cmd',
then we can get remove 'volatile' classifier in the 'wrk_cmd' definition above?  

> 
>  /* test run-time in seconds */
>  static const uint32_t run_time = 60;
> @@ -197,10 +197,12 @@ test_worker(void *arg, const char *fname, int32_t prcs)
>  	fill_ring_elm(&def_elm, UINT32_MAX);
>  	fill_ring_elm(&loc_elm, lc);
> 
> -	while (wrk_cmd != WRK_CMD_RUN) {
> -		rte_smp_rmb();
> +	/* Acquire ordering is not required as the main is not
> +	 * really releasing any data through 'wrk_cmd' to
> +	 * the worker.
> +	 */
> +	while (__atomic_load_n(&wrk_cmd, __ATOMIC_RELAXED) != WRK_CMD_RUN)
>  		rte_pause();
> -	}
> 
>  	cl = rte_rdtsc_precise();
> 
> @@ -242,7 +244,7 @@ test_worker(void *arg, const char *fname, int32_t prcs)
> 
>  		lcore_stat_update(&la->stats, 1, num, tm0 + tm1, prcs);
> 
> -	} while (wrk_cmd == WRK_CMD_RUN);
> +	} while (__atomic_load_n(&wrk_cmd, __ATOMIC_RELAXED) == WRK_CMD_RUN);
> 
>  	cl = rte_rdtsc_precise() - cl;
>  	if (prcs == 0)
> @@ -356,14 +358,12 @@ test_mt1(int (*test)(void *))
>  	}
> 
>  	/* signal worker to start test */
> -	wrk_cmd = WRK_CMD_RUN;
> -	rte_smp_wmb();
> +	__atomic_store_n(&wrk_cmd, WRK_CMD_RUN, __ATOMIC_RELEASE);
> 
>  	usleep(run_time * US_PER_S);
> 
>  	/* signal worker to start test */
> -	wrk_cmd = WRK_CMD_STOP;
> -	rte_smp_wmb();
> +	__atomic_store_n(&wrk_cmd, WRK_CMD_STOP, __ATOMIC_RELEASE);
> 
>  	/* wait for workers and collect stats. */
>  	mc = rte_lcore_id();
> --
> 2.25.1