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Date: Fri, 11 Jan 2019 15:37:09 -0800
From: Stephen Hemminger <stephen@networkplumber.org>
To: "Soni, Shivam" <shivsoni@amazon.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>, "users@dpdk.org" <users@dpdk.org>
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Subject: Re: [dpdk-dev] TX unable to enqueue packets to NIC due to no free
TX descriptor
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On Fri, 11 Jan 2019 22:10:39 +0000
"Soni, Shivam" <shivsoni@amazon.com> wrote:
> Hi All,
>=20
> We are trying to debug and fix an issue. After the deployment, in few of =
the hosts we see an issue where TX is unable to enqueue packets to NIC. On =
rebouncing or restarting our packet processor daemon, issue gets resolved.
>=20
> We are using IntelDPDK version 17.11.4 and i40e drivers.
>=20
> On looking into driver=E2=80=99s code, we found that whenever the issue i=
s happening the value for nb_tx_free is =E2=80=980=E2=80=99. And then it tr=
ies to free the buffer by calling function =E2=80=98i40e_tx_free_bufs=E2=80=
=99.
>=20
> This method returns early as the buffer its trying to free says it hasn=
=E2=80=99t finished transmitting yet. The method returns at this if conditi=
on:
>=20
> /* check DD bits on threshold descriptor */
> if ((txq->tx_ring[txq->tx_next_dd].cmd_type_offset_bsz &
> rte_cpu_to_le_64(I40E_TXD_QW1_DTYPE_MASK)) !=3D
> rte_cpu_to_le_64(I40E_TX_DESC_DTYPE_DESC_DONE)) {
> return 0;
> }
>=20
> Hence nb_tx_free remains 0.
>=20
> Our tx descriptor count is 1024.
>=20
> How can we fix this issue. Can someone help us out here please
Use bigger mbuf pool. For safety the mbuf pool has to be big enough
for Nports * (NRxd + NTxd) + NCore * (mbuf_pool_cache_size + burst_size)
Each NIC might get full receive ring and full transmit ring
and each active core might be processing a burst of packets and have
free buffers sitting in the mbuf pool cache. This doesn't account for addit=
ional
mbuf's created if doing things like reassembly, encryption, re-encapsulatio=
n, or compression
Anything smaller and your application is relying on statistical averages
to never see resource exhaustion; overcommitment