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

["Naga Harish K, S V" <s.v.naga.harish.k@intel.com>]

> -----Original Message-----
> From: Mattias Rönnblom <hofors@lysator.liu.se>
> Sent: Thursday, July 3, 2025 1:50 AM
> To: Naga Harish K, S V <s.v.naga.harish.k@intel.com>; Mattias Rönnblom
> <mattias.ronnblom@ericsson.com>; dev@dpdk.org
> Cc: Jerin Jacob <jerinj@marvell.com>; Peter Nilsson
> <peter.j.nilsson@ericsson.com>
> Subject: Re: [PATCH] event/eth_tx: prefetch mbuf headers
> 
> 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.

I think all event-types need to be equally weighted. My ask was to remove the "unlikely" for vector events.

> 
> >> {
> >> +			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
> >