Re: [PATCH] event/eth_tx: prefetch mbuf headers

["Mattias Rönnblom" <hofors@lysator.liu.se>]

On 2025-05-27 12:55, Naga Harish K, S V wrote:
> 
> 
>> -----Original Message-----
>> From: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
>> Sent: Friday, March 28, 2025 11:14 AM
>> To: dev@dpdk.org
>> Cc: Mattias Rönnblom <hofors@lysator.liu.se>; Naga Harish K, S V
>> <s.v.naga.harish.k@intel.com>; Jerin Jacob <jerinj@marvell.com>; Mattias
>> Rönnblom <mattias.ronnblom@ericsson.com>; Peter Nilsson
>> <peter.j.nilsson@ericsson.com>
>> Subject: [PATCH] event/eth_tx: prefetch mbuf headers
>>
>> Prefetch mbuf headers, resulting in ~10% throughput improvement when the
>> Ethernet RX and TX Adapters are hosted on the same core (likely ~2x in case a
>> dedicated TX core is used).
>>
>> Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
>> Tested-by: Peter Nilsson <peter.j.nilsson@ericsson.com>
>> ---
>>   lib/eventdev/rte_event_eth_tx_adapter.c | 20 ++++++++++++++++++++
>>   1 file changed, 20 insertions(+)
>>
>> diff --git a/lib/eventdev/rte_event_eth_tx_adapter.c
>> b/lib/eventdev/rte_event_eth_tx_adapter.c
>> index 67fff8b7d6..d740ae00f9 100644
>> --- a/lib/eventdev/rte_event_eth_tx_adapter.c
>> +++ b/lib/eventdev/rte_event_eth_tx_adapter.c
>> @@ -598,6 +598,12 @@ txa_process_event_vector(struct txa_service_data
>> *txa,
>>   	return nb_tx;
>>   }
>>
>> +static inline void
>> +txa_prefetch_mbuf(struct rte_mbuf *mbuf) {
>> +	rte_mbuf_prefetch_part1(mbuf);
>> +}
>> +
>>   static void
>>   txa_service_tx(struct txa_service_data *txa, struct rte_event *ev,
>>   	uint32_t n)
>> @@ -608,6 +614,20 @@ txa_service_tx(struct txa_service_data *txa, struct
>> rte_event *ev,
>>
>>   	stats = &txa->stats;
>>
>> +	for (i = 0; i < n; i++) {
>> +		struct rte_event *event = &ev[i];
>> +
>> +		if (unlikely(event->event_type & RTE_EVENT_TYPE_VECTOR))
> 
> 
> This gives a branch prediction advantage to non-vector events. Is that the intention?
> 

Yes.

>> {
>> +			struct rte_event_vector *vec = event->vec;
>> +			struct rte_mbuf **mbufs = vec->mbufs;
>> +			uint32_t k;
>> +
>> +			for (k = 0; k < vec->nb_elem; k++)
>> +				txa_prefetch_mbuf(mbufs[k]);
>> +		} else
>> +			txa_prefetch_mbuf(event->mbuf);
>> +	}
>> +
>>   	nb_tx = 0;
>>   	for (i = 0; i < n; i++) {
>>   		uint16_t port;
>> --
>> 2.43.0
>