mlx5-updates-2020-09-21
Multi packet TX descriptor support for SKBs.
This series introduces some refactoring of the regular TX data path in
mlx5 and adds the Enhanced TX MPWQE feature support. MPWQE stands for
multi-packet work queue element, and it can serve multiple packets,
reducing the PCI bandwidth spent on control traffic. It should improve
performance in scenarios where PCI is the bottleneck, and xmit_more is
signaled by the kernel. The refactoring done in this series also
improves the packet rate on its own.
MPWQE is already implemented in the XDP tx path, this series adds the
support of MPWQE for regular kernel SKB tx path.
MPWQE is supported from ConnectX-5 and onward, for legacy devices we need
to keep backward compatibility for regular (Single packet) WQE descriptor.
MPWQE is not compatible with certain offloads and features, such as TLS
offload, TSO, nonlinear SKBs. If such incompatible features are in use,
the driver gracefully falls back to non-MPWQE per SKB.
Prior to the final patch "net/mlx5e: Enhanced TX MPWQE for SKBs" that adds
the actual support, Maxim did some refactoring to the tx data path to
split it into stages and smaller helper functions that can be utilized and
reused for both legacy and new MPWQE feature.
Performance testing:
UDP performance is improved in a single stream pktgen test:
Packet rate: 16.86 Mpps (±0.15 Mpps) -> 20.94 Mpps (±0.33 Mpps)
Instructions per packet: 434 -> 329
Cycles per packet: 158 -> 123
Instructions per cycle: 2.75 -> 2.67
TCP and XDP_TX single stream tests show no performance difference.
MPWQE can reduce PCI bandwidth:
PCI Gen2, pktgen at fixed rate of 36864000 pps on 24 CPU cores:
Inbound PCI utilization with MPWQE off: 80.3%
Inbound PCI utilization with MPWQE on: 59.0%
PCI Gen3, pktgen at fixed rate of 56064000 pps on 24 CPU cores:
Inbound PCI utilization with MPWQE off: 65.4%
Inbound PCI utilization with MPWQE on: 49.3%
MPWQE can also reduce CPU load, increasing the packet rate in case of
CPU bottleneck:
PCI Gen2, pktgen at full rate on 24 CPU cores:
Packet rate with MPWQE off: 37.5 Mpps
Packet rate with MPWQE on: 49.0 Mpps
PCI Gen3, pktgen at full rate on 24 CPU cores:
Packet rate with MPWQE off: 57.0 Mpps
Packet rate with MPWQE on: 66.8 Mpps
Burst size in all pktgen tests is 32.
CPU: Intel(R) Xeon(R) CPU E5-2680 v3 @ 2.50GHz (x86_64)
NIC: Mellanox ConnectX-6 Dx
GCC 10.2.0
net/mlx5e: Enhanced TX MPWQE for SKBs
This commit adds support for Enhanced TX MPWQE feature in the regular
(SKB) data path. A MPWQE (multi-packet work queue element) can serve
multiple packets, reducing the PCI bandwidth on control traffic.
Two new stats (tx*_mpwqe_blks and tx*_mpwqe_pkts) are added. The feature
is on by default and controlled by the skb_tx_mpwqe private flag.
In a MPWQE, eseg is shared among all packets, so eseg-based offloads
(IPSEC, GENEVE, checksum) run on a separate eseg that is compared to the
eseg of the current MPWQE session to decide if the new packet can be
added to the same session.
MPWQE is not compatible with certain offloads and features, such as TLS
offload, TSO, nonlinear SKBs. If such incompatible features are in use,
the driver gracefully falls back to non-MPWQE.
This change has no performance impact in TCP single stream test and
XDP_TX single stream test.
UDP pktgen, 64-byte packets, single stream, MPWQE off:
Packet rate: 16.96 Mpps (±0.12 Mpps) -> 17.01 Mpps (±0.20 Mpps)
Instructions per packet: 421 -> 429
Cycles per packet: 156 -> 161
Instructions per cycle: 2.70 -> 2.67
UDP pktgen, 64-byte packets, single stream, MPWQE on:
Packet rate: 16.96 Mpps (±0.12 Mpps) -> 20.94 Mpps (±0.33 Mpps)
Instructions per packet: 421 -> 329
Cycles per packet: 156 -> 123
Instructions per cycle: 2.70 -> 2.67
Enabling MPWQE can reduce PCI bandwidth:
PCI Gen2, pktgen at fixed rate of 36864000 pps on 24 CPU cores:
Inbound PCI utilization with MPWQE off: 80.3%
Inbound PCI utilization with MPWQE on: 59.0%
PCI Gen3, pktgen at fixed rate of 56064000 pps on 24 CPU cores:
Inbound PCI utilization with MPWQE off: 65.4%
Inbound PCI utilization with MPWQE on: 49.3%
Enabling MPWQE can also reduce CPU load, increasing the packet rate in
case of CPU bottleneck:
PCI Gen2, pktgen at full rate on 24 CPU cores:
Packet rate with MPWQE off: 37.5 Mpps
Packet rate with MPWQE on: 49.0 Mpps
PCI Gen3, pktgen at full rate on 24 CPU cores:
Packet rate with MPWQE off: 57.0 Mpps
Packet rate with MPWQE on: 66.8 Mpps
Burst size in all pktgen tests is 32.
CPU: Intel(R) Xeon(R) CPU E5-2680 v3 @ 2.50GHz (x86_64)
NIC: Mellanox ConnectX-6 Dx
GCC 10.2.0
Signed-off-by: Maxim Mikityanskiy <maximmi@mellanox.com>
Reviewed-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
11 files changed
