[PATCH 1/2] baseband/fpga_5gnr_fec: use new barrier API

[Maxime Coquelin]

Hello,

On 2/22/24 19:05, Chautru, Nicolas wrote:
> Hi Maxime,
> 
> Why would we change this here and now? Is the intent not to use new suggested semantics for new patches only?

The pull request was rejected because of the use of such barrier, which 
is reported by checkpatch.

### [PATCH] baseband/fpga_5gnr_fec: add AGX100 support
Warning in drivers/baseband/fpga_5gnr_fec/rte_fpga_5gnr_fec.c:
Using rte_smp_[r/w]mb

> Are all DPDK drivers being changed?

My understanding is that for now, only new occurrences are prohibited,
can you confirm Tyler?

If so we could only change for now the patch adding ACX100.
But... I preferred doing the changes for all bbdev drivers for
consistency.

> I am unsure we would want to change these drivers, this is kind of risk introduced by code churn that gets ecosystem unwilling to move to latest version.

I think it is better to change now that we are far from the next LTS.

> These memory barriers issues are awful to troubleshoot or properly validate, so personally quite reluctant to change.

If I disassemble fpga_dequeue_enc() with and without the patch, I cannot
spot a difference.

Thomas, are you waiting for this series to be applied to take the pull
request that was initially for -rc1?

Thanks,
Maxime

> Thanks
> Nic
> 
>> -----Original Message-----
>> From: Maxime Coquelin <maxime.coquelin at redhat.com>
>> Sent: Thursday, February 22, 2024 8:21 AM
>> To: dev at dpdk.org; Chautru, Nicolas <nicolas.chautru at intel.com>; Vargas,
>> Hernan <hernan.vargas at intel.com>; Marchand, David
>> <david.marchand at redhat.com>; thomas at monjalon.net;
>> roretzla at linux.microsoft.com
>> Cc: Maxime Coquelin <maxime.coquelin at redhat.com>
>> Subject: [PATCH 1/2] baseband/fpga_5gnr_fec: use new barrier API
>>
>> rte_smp_rmb() is deprecated, use the new API instead as suggested in
>> rte_atomic header.
>>
>> Signed-off-by: Maxime Coquelin <maxime.coquelin at redhat.com>
>> ---
>>   drivers/baseband/fpga_5gnr_fec/rte_fpga_5gnr_fec.c | 8 ++++----
>>   1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/baseband/fpga_5gnr_fec/rte_fpga_5gnr_fec.c
>> b/drivers/baseband/fpga_5gnr_fec/rte_fpga_5gnr_fec.c
>> index efc1d3a772..314c87350e 100644
>> --- a/drivers/baseband/fpga_5gnr_fec/rte_fpga_5gnr_fec.c
>> +++ b/drivers/baseband/fpga_5gnr_fec/rte_fpga_5gnr_fec.c
>> @@ -2661,7 +2661,7 @@ vc_5gnr_dequeue_ldpc_enc_one_op_cb(struct
>> fpga_5gnr_queue *q, struct rte_bbdev_e
>>   		return -1;
>>
>>   	/* make sure the response is read atomically */
>> -	rte_smp_rmb();
>> +	rte_atomic_thread_fence(rte_memory_order_acquire);
>>
>>   	rte_bbdev_log_debug("DMA response desc %p", desc);
>>
>> @@ -2690,7 +2690,7 @@ agx100_dequeue_ldpc_enc_one_op_cb(struct
>> fpga_5gnr_queue *q, struct rte_bbdev_en
>>   		return -1;
>>
>>   	/* make sure the response is read atomically. */
>> -	rte_smp_rmb();
>> +	rte_atomic_thread_fence(rte_memory_order_acquire);
>>
>>   	rte_bbdev_log_debug("DMA response desc %p", desc);
>>
>> @@ -2722,7 +2722,7 @@ vc_5gnr_dequeue_ldpc_dec_one_op_cb(struct
>> fpga_5gnr_queue *q, struct rte_bbdev_d
>>   		return -1;
>>
>>   	/* make sure the response is read atomically */
>> -	rte_smp_rmb();
>> +	rte_atomic_thread_fence(rte_memory_order_acquire);
>>
>>   #ifdef RTE_LIBRTE_BBDEV_DEBUG
>>   	vc_5gnr_print_dma_dec_desc_debug_info(desc);
>> @@ -2768,7 +2768,7 @@ agx100_dequeue_ldpc_dec_one_op_cb(struct
>> fpga_5gnr_queue *q, struct rte_bbdev_de
>>   		return -1;
>>
>>   	/* make sure the response is read atomically. */
>> -	rte_smp_rmb();
>> +	rte_atomic_thread_fence(rte_memory_order_acquire);
>>
>>   #ifdef RTE_LIBRTE_BBDEV_DEBUG
>>   	agx100_print_dma_dec_desc_debug_info(desc);
>> --
>> 2.43.0
>