Re: [dpdk-dev] [PATCH] vdpa/mlx5: fix polling threads scheduling

["Xueming(Steven) Li" <xuemingl@nvidia.com>]

>-----Original Message-----
>From: dev <dev-bounces@dpdk.org> On Behalf Of Maxime Coquelin
>Sent: Monday, February 8, 2021 7:17 PM
>To: Matan Azrad <matan@nvidia.com>; dev@dpdk.org
>Subject: Re: [dpdk-dev] [PATCH] vdpa/mlx5: fix polling threads scheduling
>
>
>
>On 2/8/21 10:28 AM, Matan Azrad wrote:
>> When the event mode is with 0 fixed delay, the polling-thread will
>> never give-up CPU.
>>
>> So, when multi-polling-threads are active, the context-switch between
>> them will be managed by the system which may affect latency according
>> to the time-out decided by the system.
>>
>> In order to fix multi-devices polling thread scheduling, this patch
>> forces rescheduling for each CQ poll iteration.
>>
>> Move the polling thread to SCHED_RR mode with maximum priority to
>> complete the fairness.
>>
>> Fixes: 6956a48cabbb ("vdpa/mlx5: set polling mode default delay to
>> zero")
>>
>> Signed-off-by: Matan Azrad <matan@nvidia.com>
>> ---
>>  drivers/vdpa/mlx5/mlx5_vdpa_event.c | 16 ++++++++++++++++
>>  1 file changed, 16 insertions(+)
>>
>> diff --git a/drivers/vdpa/mlx5/mlx5_vdpa_event.c
>> b/drivers/vdpa/mlx5/mlx5_vdpa_event.c
>> index 0f635ff..86adc86 100644
>> --- a/drivers/vdpa/mlx5/mlx5_vdpa_event.c
>> +++ b/drivers/vdpa/mlx5/mlx5_vdpa_event.c
>> @@ -232,6 +232,9 @@
>>  	}
>>  	if (priv->timer_delay_us)
>>  		usleep(priv->timer_delay_us);
>> +	else
>> +		/* Give-up CPU to improve polling threads scheduling. */
>> +		pthread_yield();
>>  }
>>
>>  static void *
>> @@ -500,6 +503,9 @@
>>  	rte_cpuset_t cpuset;
>>  	pthread_attr_t attr;
>>  	char name[16];
>> +	const struct sched_param sp = {
>> +		.sched_priority = sched_get_priority_max(SCHED_RR),
>> +	};
>>
>>  	if (!priv->eventc)
>>  		/* All virtqs are in poll mode. */
>> @@ -520,6 +526,16 @@
>>  			DRV_LOG(ERR, "Failed to set thread affinity.");
>>  			return -1;
>>  		}
>> +		ret = pthread_attr_setschedpolicy(&attr, SCHED_RR);
>> +		if (ret) {
>> +			DRV_LOG(ERR, "Failed to set thread sched policy = RR.");
>> +			return -1;
>> +		}
>> +		ret = pthread_attr_setschedparam(&attr, &sp);
>> +		if (ret) {
>> +			DRV_LOG(ERR, "Failed to set thread priority.");
>> +			return -1;
>> +		}
>>  		ret = pthread_create(&priv->timer_tid, &attr,
>>  				     mlx5_vdpa_poll_handle, (void *)priv);
>>  		if (ret) {
>>
>
>Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

Acked-by: Xueming Li <xuemingl@mellanox.com>