Re: [dpdk-dev] [PATCH v1 01/12] test/pmd_perf: use compiler atomic builtins for polling sync

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

<snip>

> 
> Convert rte_atomic usages to compiler atomic built-ins for polling sync in
> pmd_perf test cases.
> 
> Signed-off-by: Joyce Kong <joyce.kong@arm.com>
> Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> ---
>  app/test/test_pmd_perf.c | 12 +++++-------
>  1 file changed, 5 insertions(+), 7 deletions(-)
> 
> diff --git a/app/test/test_pmd_perf.c b/app/test/test_pmd_perf.c index
> 3a248d512c..41ef001b90 100644
> --- a/app/test/test_pmd_perf.c
> +++ b/app/test/test_pmd_perf.c
> @@ -10,7 +10,6 @@
>  #include <rte_cycles.h>
>  #include <rte_ethdev.h>
>  #include <rte_byteorder.h>
> -#include <rte_atomic.h>
>  #include <rte_malloc.h>
>  #include "packet_burst_generator.h"
>  #include "test.h"
> @@ -526,7 +525,7 @@ main_loop(__rte_unused void *args)
>  	return 0;
>  }
> 
> -static rte_atomic64_t start;
> +static uint64_t start;
> 
>  static inline int
>  poll_burst(void *args)
> @@ -564,8 +563,7 @@ poll_burst(void *args)
>  		num[portid] = pkt_per_port;
>  	}
> 
> -	while (!rte_atomic64_read(&start))
> -		;
> +	rte_wait_until_equal_64(&start, 1, __ATOMIC_RELAXED);
This needs to be ACQUIRE. Please see comments below for function 'exec_burst'.

> 
>  	cur_tsc = rte_rdtsc();
>  	while (total) {
> @@ -617,7 +615,7 @@ exec_burst(uint32_t flags, int lcore)
>  	pkt_per_port = MAX_TRAFFIC_BURST;
>  	num = pkt_per_port * conf->nb_ports;
> 
> -	rte_atomic64_init(&start);
> +	__atomic_store_n(&start, 0, __ATOMIC_RELAXED);
> 
>  	/* start polling thread, but not actually poll yet */
>  	rte_eal_remote_launch(poll_burst,
> @@ -625,7 +623,7 @@ exec_burst(uint32_t flags, int lcore)
> 
>  	/* Only when polling first */
>  	if (flags == SC_BURST_POLL_FIRST)
> -		rte_atomic64_set(&start, 1);
> +		__atomic_store_n(&start, 1, __ATOMIC_RELAXED);
This line can be combined with initialization of 'start'. i.e.
if (flags == SC_BURST_POLL_FIRST) {
	__atomic_store_n(&start, 1, __ATOMIC_RELAXED);
} else {
	__atomic_store_n(&start, 0, __ATOMIC_RELAXED);
}
It is ok to use RELAXED here as it is part of initialization and 'rte_eal_remote_launch' will ensure that the store to 'start' is visible to the worker thread.

> 
>  	/* start xmit */
>  	i = 0;
> @@ -642,7 +640,7 @@ exec_burst(uint32_t flags, int lcore)
> 
>  	/* only when polling second  */
>  	if (flags == SC_BURST_XMIT_FIRST)
> -		rte_atomic64_set(&start, 1);
> +		__atomic_store_n(&start, 1, __ATOMIC_RELAXED);
This store should happen after transmitting the packets. It is better to use RELEASE here.

> 
>  	/* wait for polling finished */
>  	diff_tsc = rte_eal_wait_lcore(lcore);
> --
> 2.17.1