ixgbe: fix Tx hang when RS distance exceeds HW limit

One of the ways to reproduce the issue:

testpmd <EAL-OPTIONS> -- -i --txqflags=0
testpmd> set fwd txonly
testpmd> set txpkts 64,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4
testpmd> set txsplit rand
testpmd> start

After some time TX on ixgbe queue will hang,
and all packet transmission on that queue will stop.

This bug was first reported and investigated by
Vlad Zolotarov <vladz@cloudius-systems.com>:
"We can reproduce this issue when stressed the xmit path with a lot of highly
fragmented TCP frames (packets with up to 33 fragments with non-headers
fragments as small as 4 bytes) with all offload features enabled."

The root cause is that ixgbe_xmit_pkts() in some cases violates the HW rule
that the distance between TDs with RS bit set should not exceed 40 TDs.

>From the latest 82599 spec update:
"When WTHRESH is set to zero, the software device driver should set the RS bit
in the Tx descriptors with the EOP bit set and at least once in the 40
descriptors."

The fix is to make sure that the distance between TDs with RS bit set
would never exceed HW limit.
As part of that fix, tx_rs_thresh for ixgbe PMD is not allowed to be greater
then to 32 to comply with HW restrictions.

With that fix slight slowdown for the full-featured ixgbe TX path
might be observed (from our testing - up to 4%).

ixgbe simple TX path is unaffected by that patch.

Reported-by: Vlad Zolotarov <vladz@cloudius-systems.com>
Signed-off-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Acked-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>

diff --git a/app/test/test_pmd_perf.c b/app/test/test_pmd_perf.c
index 1fd6843cdff7a13e71038cc90a9d593461b819a4..ef9262c3ba665c87005bc0182f5aa078f1e2e372 100644 (file)
--- a/app/test/test_pmd_perf.c
+++ b/app/test/test_pmd_perf.c
@@ -841,10 +841,10 @@ test_set_rxtx_conf(cmdline_fixed_string_t mode)
                port_conf.rxmode.enable_scatter = 0;
                return 0;
        } else if (!strcmp(mode, "scalar")) {
-               /* bulk alloc rx, simple tx */
-               tx_conf.txq_flags = 0xf01;
-               tx_conf.tx_rs_thresh = 128;
-               tx_conf.tx_free_thresh = 128;
+               /* bulk alloc rx, full-featured tx */
+               tx_conf.txq_flags = 0;
+               tx_conf.tx_rs_thresh = 32;
+               tx_conf.tx_free_thresh = 32;
                port_conf.rxmode.hw_ip_checksum = 1;
                port_conf.rxmode.enable_scatter = 0;
                return 0;

diff --git a/doc/guides/rel_notes/release_2_2.rst b/doc/guides/rel_notes/release_2_2.rst
index eaa906cc9eb3e9f4df835e3177d8c0718ba700e0..5636aad52a4352f4f5703a5b6c71a3d68c6562b4 100644 (file)
--- a/doc/guides/rel_notes/release_2_2.rst
+++ b/doc/guides/rel_notes/release_2_2.rst
@@ -134,6 +134,13 @@ Drivers
 
   VF needs the PF interrupt support initialized even if not started.
 
+* **ixgbe: Fixed TX hang when RS distance exceeds HW limit.**
+
+  Fixed an issue when TX queue can hang when a lot of highly fragmented
+  packets have to be sent.
+  As part of that fix, tx_rs_thresh for ixgbe PMD is not allowed to be greater
+  then to 32 to comply with HW restrictions.
+
 * **i40e: Fixed base driver allocation when not using first numa node.**
 
   Fixed i40e issue that occurred when a DPDK application didn't initialize

diff --git a/drivers/net/ixgbe/ixgbe_rxtx.c b/drivers/net/ixgbe/ixgbe_rxtx.c
index 55611950bc8328228274739267ae6d206e82e4c3..ca6fb693da3277bef65851a985355878533ad69e 100644 (file)
--- a/drivers/net/ixgbe/ixgbe_rxtx.c
+++ b/drivers/net/ixgbe/ixgbe_rxtx.c
@@ -572,7 +572,7 @@ ixgbe_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
        struct ixgbe_tx_entry *sw_ring;
        struct ixgbe_tx_entry *txe, *txn;
        volatile union ixgbe_adv_tx_desc *txr;
-       volatile union ixgbe_adv_tx_desc *txd;
+       volatile union ixgbe_adv_tx_desc *txd, *txp;
        struct rte_mbuf     *tx_pkt;
        struct rte_mbuf     *m_seg;
        uint64_t buf_dma_addr;
@@ -595,6 +595,7 @@ ixgbe_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
        txr     = txq->tx_ring;
        tx_id   = txq->tx_tail;
        txe = &sw_ring[tx_id];
+       txp = NULL;
 
        /* Determine if the descriptor ring needs to be cleaned. */
        if (txq->nb_tx_free < txq->tx_free_thresh)
@@ -638,6 +639,12 @@ ixgbe_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
                 */
                nb_used = (uint16_t)(tx_pkt->nb_segs + new_ctx);
 
+               if (txp != NULL &&
+                               nb_used + txq->nb_tx_used >= txq->tx_rs_thresh)
+                       /* set RS on the previous packet in the burst */
+                       txp->read.cmd_type_len |=
+                               rte_cpu_to_le_32(IXGBE_TXD_CMD_RS);
+
                /*
                 * The number of descriptors that must be allocated for a
                 * packet is the number of segments of that packet, plus 1
@@ -840,10 +847,18 @@ ixgbe_xmit_pkts(void *tx_queue, struct rte_mbuf **tx_pkts,
 
                        /* Update txq RS bit counters */
                        txq->nb_tx_used = 0;
-               }
+                       txp = NULL;
+               } else
+                       txp = txd;
+
                txd->read.cmd_type_len |= rte_cpu_to_le_32(cmd_type_len);
        }
+
 end_of_tx:
+       /* set RS on last packet in the burst */
+       if (txp != NULL)
+               txp->read.cmd_type_len |= rte_cpu_to_le_32(IXGBE_TXD_CMD_RS);
+
        rte_wmb();
 
        /*
@@ -2019,9 +2034,16 @@ ixgbe_dev_tx_queue_setup(struct rte_eth_dev *dev,
                        tx_conf->tx_free_thresh : DEFAULT_TX_FREE_THRESH);
        if (tx_rs_thresh >= (nb_desc - 2)) {
                PMD_INIT_LOG(ERR, "tx_rs_thresh must be less than the number "
-                            "of TX descriptors minus 2. (tx_rs_thresh=%u "
-                            "port=%d queue=%d)", (unsigned int)tx_rs_thresh,
-                            (int)dev->data->port_id, (int)queue_idx);
+                       "of TX descriptors minus 2. (tx_rs_thresh=%u "
+                       "port=%d queue=%d)", (unsigned int)tx_rs_thresh,
+                       (int)dev->data->port_id, (int)queue_idx);
+               return -(EINVAL);
+       }
+       if (tx_rs_thresh > DEFAULT_TX_RS_THRESH) {
+               PMD_INIT_LOG(ERR, "tx_rs_thresh must be less or equal than %u. "
+                       "(tx_rs_thresh=%u port=%d queue=%d)",
+                       DEFAULT_TX_RS_THRESH, (unsigned int)tx_rs_thresh,
+                       (int)dev->data->port_id, (int)queue_idx);
                return -(EINVAL);
        }
        if (tx_free_thresh >= (nb_desc - 3)) {