> -----Original Message-----
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Hiroshi Shimamoto
> Sent: Tuesday, September 30, 2014 7:15 PM
> To: dev at dpdk.org
> Cc: Hayato Momma
> Subject: [dpdk-dev] [memnic PATCH v2 6/7] pmd: add branch hint in recv/xmit
>
> From: Hiroshi Shimamoto <h-shimamoto at ct.jp.nec.com>
>
> To reduce instruction cache miss, add branch condition hints into
> recv/xmit functions. This improves a bit performance.
>
> We can see performance improvements with memnic-tester.
> Using Xeon E5-2697 v2 @ 2.70GHz, 4 vCPU.
> size | before | after
> 64 | 5.54Mpps | 5.55Mpps
> 128 | 5.46Mpps | 5.44Mpps
> 256 | 5.21Mpps | 5.22Mpps
> 512 | 4.50Mpps | 4.52Mpps
> 1024 | 3.71Mpps | 3.73Mpps
> 1280 | 3.21Mpps | 3.22Mpps
> 1518 | 2.92Mpps | 2.93Mpps
>
> Signed-off-by: Hiroshi Shimamoto <h-shimamoto at ct.jp.nec.com>
> Reviewed-by: Hayato Momma <h-momma at ce.jp.nec.com>
> ---
> pmd/pmd_memnic.c | 18 +++++++++---------
> 1 file changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/pmd/pmd_memnic.c b/pmd/pmd_memnic.c
> index 7fc3093..875d3ea 100644
> --- a/pmd/pmd_memnic.c
> +++ b/pmd/pmd_memnic.c
> @@ -289,26 +289,26 @@ static uint16_t memnic_recv_pkts(void *rx_queue,
> int idx, next;
> struct rte_eth_stats *st = &adapter->stats[rte_lcore_id()];
>
> - if (!adapter->nic->hdr.valid)
> + if (unlikely(!adapter->nic->hdr.valid))
> return 0;
>
> pkts = bytes = errs = 0;
> idx = adapter->up_idx;
> for (nr = 0; nr < nb_pkts; nr++) {
> p = &data->packets[idx];
> - if (p->status != MEMNIC_PKT_ST_FILLED)
> + if (unlikely(p->status != MEMNIC_PKT_ST_FILLED))
> break;
> /* prefetch the next area */
> next = idx;
> - if (++next >= MEMNIC_NR_PACKET)
> + if (unlikely(++next >= MEMNIC_NR_PACKET))
On IA, compiler can use add, cmp and cmov to avoid branch.
But If MEMNIC_NR_PACKET is always power of 2,
it is better just next = (next + 1) & (MEMNIC_NR_PACKET - 1)
> next = 0;
> rte_prefetch0(&data->packets[next]);
> - if (p->len > framesz) {
> + if (unlikely(p->len > framesz)) {
> errs++;
> goto drop;
> }
> mb = rte_pktmbuf_alloc(adapter->mp);
> - if (!mb)
> + if (unlikely(!mb))
> break;
>
> rte_memcpy(rte_pktmbuf_mtod(mb, void *), p->data, p->len);
> @@ -350,7 +350,7 @@ static uint16_t memnic_xmit_pkts(void *tx_queue,
> uint64_t pkts, bytes, errs;
> uint32_t framesz = adapter->framesz;
>
> - if (!adapter->nic->hdr.valid)
> + if (unlikely(!adapter->nic->hdr.valid))
> return 0;
>
> pkts = bytes = errs = 0;
> @@ -360,7 +360,7 @@ static uint16_t memnic_xmit_pkts(void *tx_queue,
> struct rte_mbuf *sg;
> void *ptr;
>
> - if (pkt_len > framesz) {
> + if (unlikely(pkt_len > framesz)) {
> errs++;
> break;
> }
> @@ -379,7 +379,7 @@ retry:
> goto retry;
> }
>
> - if (idx != ACCESS_ONCE(adapter->down_idx)) {
> + if (unlikely(idx != ACCESS_ONCE(adapter->down_idx))) {
> /*
> * host freed this and got false positive,
> * need to recover the status and retry.
> @@ -388,7 +388,7 @@ retry:
> goto retry;
> }
>
> - if (++idx >= MEMNIC_NR_PACKET)
> + if (unlikely(++idx >= MEMNIC_NR_PACKET))
> idx = 0;
> adapter->down_idx = idx;
>
> --
> 1.8.3.1
