Alexander Kozyrev <akozy...@mellanox.com> writes: <...> > Subject: RE: [dpdk-dev] [PATCH v3] net/mlx5: relaxed ordering for multi- > packet RQ buffer refcnt > > Hi Phil Yang, we noticed that this patch gives us 10% of performance > degradation on ARM. > x86 seems to be unaffected though. Do you know what may be the reason > of this behavior?
Hi Alexander, Thanks for your feedback. This patch removed some expensive memory barriers on aarch64, it should get better performance. I am not sure the root cause of this degradation now, I will start the investigation. We can profiling this issue together. Could you share your test case(including your testbed configuration) with us? Thanks, Phil > > Regards, > Alex > > > -----Original Message----- > > From: dev <dev-boun...@dpdk.org> On Behalf Of Phil Yang > > Sent: Sunday, July 12, 2020 23:02 > > To: Matan Azrad <ma...@mellanox.com>; Shahaf Shuler > > <shah...@mellanox.com>; Slava Ovsiienko <viachesl...@mellanox.com> > > Cc: Honnappa Nagarahalli <honnappa.nagaraha...@arm.com>; > > d...@linux.vnet.ibm.com; nd <n...@arm.com>; Phil Yang > <phil.y...@arm.com>; > > dev@dpdk.org; nd <n...@arm.com> > > Subject: Re: [dpdk-dev] [PATCH v3] net/mlx5: relaxed ordering for multi- > packet > > RQ buffer refcnt > > > > Hi, > > > > We are also doing C11 atomics converting for other components. > > Your insight would be much appreciated. > > > > Thanks, > > Phil Yang > > > > > -----Original Message----- > > > From: dev <dev-boun...@dpdk.org> On Behalf Of Phil Yang > > > Sent: Tuesday, June 23, 2020 4:27 PM > > > To: dev@dpdk.org > > > Cc: ma...@mellanox.com; shah...@mellanox.com; > > > viachesl...@mellanox.com; Honnappa Nagarahalli > > > <honnappa.nagaraha...@arm.com>; d...@linux.vnet.ibm.com; nd > > > <n...@arm.com> > > > Subject: [dpdk-dev] [PATCH v3] net/mlx5: relaxed ordering for > > > multi-packet RQ buffer refcnt > > > > > > Use c11 atomics with explicit ordering instead of the rte_atomic ops > > > which enforce unnecessary barriers on aarch64. > > > > > > Signed-off-by: Phil Yang <phil.y...@arm.com> > > > --- > > > v3: > > > Split from the patchset: > > > > https://eur03.safelinks.protection.outlook.com/?url=http%3A%2F%2Fpatch > > > > > > work.dpdk.org%2Fcover%2F68159%2F&data=02%7C01%7Cakozyrev%40 > m > > ellano > > > > > > x.com%7C1e3dc839a3604924fdf208d826d934ad%7Ca652971c7d2e4d9ba6a4d > 1 > > 49256 > > > > > > f461b%7C0%7C0%7C637302061620808255&sdata=mRXbgPi6HyrVtP04Vl > 7 > > Bx8lD0 > > > trVP7noQlpOD7gBoTQ%3D&reserved=0 > > > > > > drivers/net/mlx5/mlx5_rxq.c | 2 +- > > > drivers/net/mlx5/mlx5_rxtx.c | 16 +++++++++------- > > > drivers/net/mlx5/mlx5_rxtx.h | 2 +- > > > 3 files changed, 11 insertions(+), 9 deletions(-) > > > > > > diff --git a/drivers/net/mlx5/mlx5_rxq.c b/drivers/net/mlx5/mlx5_rxq.c > > > index dda0073..7f487f1 100644 > > > --- a/drivers/net/mlx5/mlx5_rxq.c > > > +++ b/drivers/net/mlx5/mlx5_rxq.c > > > @@ -1545,7 +1545,7 @@ mlx5_mprq_buf_init(struct rte_mempool *mp, > void > > > *opaque_arg, > > > > > > memset(_m, 0, sizeof(*buf)); > > > buf->mp = mp; > > > - rte_atomic16_set(&buf->refcnt, 1); > > > + __atomic_store_n(&buf->refcnt, 1, __ATOMIC_RELAXED); > > > for (j = 0; j != strd_n; ++j) { > > > shinfo = &buf->shinfos[j]; > > > shinfo->free_cb = mlx5_mprq_buf_free_cb; diff --git > > > a/drivers/net/mlx5/mlx5_rxtx.c b/drivers/net/mlx5/mlx5_rxtx.c index > > > e4106bf..f0eda88 100644 > > > --- a/drivers/net/mlx5/mlx5_rxtx.c > > > +++ b/drivers/net/mlx5/mlx5_rxtx.c > > > @@ -1595,10 +1595,11 @@ mlx5_mprq_buf_free_cb(void *addr > > __rte_unused, > > > void *opaque) { > > > struct mlx5_mprq_buf *buf = opaque; > > > > > > - if (rte_atomic16_read(&buf->refcnt) == 1) { > > > + if (__atomic_load_n(&buf->refcnt, __ATOMIC_RELAXED) == 1) { > > > rte_mempool_put(buf->mp, buf); > > > - } else if (rte_atomic16_add_return(&buf->refcnt, -1) == 0) { > > > - rte_atomic16_set(&buf->refcnt, 1); > > > + } else if (unlikely(__atomic_sub_fetch(&buf->refcnt, 1, > > > + __ATOMIC_RELAXED) == 0)) { > > > + __atomic_store_n(&buf->refcnt, 1, __ATOMIC_RELAXED); > > > rte_mempool_put(buf->mp, buf); > > > } > > > } > > > @@ -1678,7 +1679,8 @@ mlx5_rx_burst_mprq(void *dpdk_rxq, struct > > > rte_mbuf **pkts, uint16_t pkts_n) > > > > > > if (consumed_strd == strd_n) { > > > /* Replace WQE only if the buffer is still in use. */ > > > - if (rte_atomic16_read(&buf->refcnt) > 1) { > > > + if (__atomic_load_n(&buf->refcnt, > > > + __ATOMIC_RELAXED) > 1) { > > > mprq_buf_replace(rxq, rq_ci & wq_mask, > > strd_n); > > > /* Release the old buffer. */ > > > mlx5_mprq_buf_free(buf); > > > @@ -1790,9 +1792,9 @@ mlx5_rx_burst_mprq(void *dpdk_rxq, struct > > > rte_mbuf **pkts, uint16_t pkts_n) > > > void *buf_addr; > > > > > > /* Increment the refcnt of the whole chunk. */ > > > - rte_atomic16_add_return(&buf->refcnt, 1); > > > - MLX5_ASSERT((uint16_t)rte_atomic16_read(&buf- > > > >refcnt) <= > > > - strd_n + 1); > > > + __atomic_add_fetch(&buf->refcnt, 1, > > > __ATOMIC_ACQUIRE); > > > + MLX5_ASSERT(__atomic_load_n(&buf->refcnt, > > > + __ATOMIC_RELAXED) <= strd_n + 1); > > > buf_addr = RTE_PTR_SUB(addr, > > > RTE_PKTMBUF_HEADROOM); > > > /* > > > * MLX5 device doesn't use iova but it is necessary in > a > > diff > > > --git a/drivers/net/mlx5/mlx5_rxtx.h b/drivers/net/mlx5/mlx5_rxtx.h > > > index 26621ff..0fc15f3 100644 > > > --- a/drivers/net/mlx5/mlx5_rxtx.h > > > +++ b/drivers/net/mlx5/mlx5_rxtx.h > > > @@ -78,7 +78,7 @@ struct rxq_zip { > > > /* Multi-Packet RQ buffer header. */ > > > struct mlx5_mprq_buf { > > > struct rte_mempool *mp; > > > - rte_atomic16_t refcnt; /* Atomically accessed refcnt. */ > > > + uint16_t refcnt; /* Atomically accessed refcnt. */ > > > uint8_t pad[RTE_PKTMBUF_HEADROOM]; /* Headroom for the first > > packet. > > > */ > > > struct rte_mbuf_ext_shared_info shinfos[]; > > > /* > > > -- > > > 2.7.4
