> -----Original Message-----
> From: Ferruh Yigit <ferruh.yi...@xilinx.com>
> Sent: Thursday, May 19, 2022 1:06 AM
> To: Joyce Kong <joyce.k...@arm.com>; Jakub Grajciar <jgraj...@cisco.com>
> Cc: Ruifeng Wang <ruifeng.w...@arm.com>; dev@dpdk.org; nd
> <n...@arm.com>
> Subject: Re: [PATCH v1 1/2] net/memif: add a Rx fast path
>
> On 5/17/2022 11:51 AM, Joyce Kong wrote:
> > For memif non-zero-copy mode, there is a branch to compare
> > the mbuf and memif buffer size during memory copying. Add
> > a fast memory copy path by removing this branch with mbuf
> > and memif buffer size defined at compile time. The removal
> > of the branch leads to considerable performance uplift.
> >
> > When memif <= buffer size, Rx chooses the fast memcpy path,
> > otherwise it would choose the original path.
> >
> > Test with 1p1q on Ampere Altra AArch64 server,
> > --------------------------------------------
> > buf size | memif <= mbuf | memif > mbuf |
> > --------------------------------------------
> > non-zc gain | 4.30% | -0.52% |
> > --------------------------------------------
> > zc gain | 2.46% | 0.70% |
> > --------------------------------------------
> >
> > Test with 1p1q on Cascade Lake Xeon X86server,
> > -------------------------------------------
> > buf size | memif <= mbuf | memif > mbuf |
> > -------------------------------------------
> > non-zc gain | 2.13% | -1.40% |
> > -------------------------------------------
> > zc gain | 0.18% | 0.48% |
> > -------------------------------------------
> >
> > Signed-off-by: Joyce Kong <joyce.k...@arm.com>
>
> <...>
>
> > + } else {
> > + while (n_slots && n_rx_pkts < nb_pkts) {
> > + mbuf_head = rte_pktmbuf_alloc(mq->mempool);
> > + if (unlikely(mbuf_head == NULL))
> > + goto no_free_bufs;
> > + mbuf = mbuf_head;
> > + mbuf->port = mq->in_port;
> > +
> > +next_slot2:
> > + s0 = cur_slot & mask;
> > + d0 = &ring->desc[s0];
> >
> > - rte_memcpy(rte_pktmbuf_mtod_offset(mbuf, void *,
> > - dst_off),
> > - (uint8_t *)memif_get_buffer(proc_private, d0)
> +
> > - src_off, cp_len);
> > + src_len = d0->length;
> > + dst_off = 0;
> > + src_off = 0;
>
> Hi Joyce, Jakub,
>
> Something doesn't look right in the original code (not in this patch),
> can you please help me check if I am missing something?
>
> For the memif buffer segmented case, first buffer will be copied to
> mbuf, 'dst_off' increased and jump back to process next memif segment:
>
> + d0
> |
> v
> +++ +-+
> |a+->+b|
> +-+ +-+
>
> +---+
> |a |
> +-+-+
> ^
> |
> + dst_off
>
> "
> if (d0->flags & MEMIF_DESC_FLAG_NEXT)
> goto next_slot;
> "
>
> But here 'dst_off' set back to '0', wont this cause next memif buffer
> segment to write to beginning of mbuf overwriting previous data?
>
> Thanks,
> Ferruh
Hi Ferruh,
Agree with you here, and sorry I didn’t notice it before. Perhaps moving
'det_off = 0' to the line above 'next_slot' would solve the overwriting?
Best Regards,
Joyce
