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Documentation: networking: add RSS information

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Signed-off-by: Madalin Bucur <madalin.bucur@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Madalin Bucur 2017-08-27 16:13:42 +03:00 committed by David S. Miller
parent 056057e288
commit 0659191630
1 changed files with 67 additions and 1 deletions
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68
Documentation/networking/dpaa.txt
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@ -13,6 +13,7 @@ Contents
- Configuring DPAA Ethernet in your kernel
- DPAA Ethernet Frame Processing
- DPAA Ethernet Features
- DPAA IRQ Affinity and Receive Side Scaling
- Debugging
DPAA Ethernet Overview
@ -147,7 +148,10 @@ gradually.
The driver has Rx and Tx checksum offloading for UDP and TCP. Currently the Rx
checksum offload feature is enabled by default and cannot be controlled through
ethtool.
ethtool. Also, rx-flow-hash and rx-hashing was added. The addition of RSS
provides a big performance boost for the forwarding scenarios, allowing
different traffic flows received by one interface to be processed by different
CPUs in parallel.
The driver has support for multiple prioritized Tx traffic classes. Priorities
range from 0 (lowest) to 3 (highest). These are mapped to HW workqueues with
@ -166,6 +170,68 @@ classes as follows:
tc qdisc add dev <int> root handle 1: \
mqprio num_tc 4 map 0 0 0 0 1 1 1 1 2 2 2 2 3 3 3 3 hw 1
DPAA IRQ Affinity and Receive Side Scaling
==========================================
Traffic coming on the DPAA Rx queues or on the DPAA Tx confirmation
queues is seen by the CPU as ingress traffic on a certain portal.
The DPAA QMan portal interrupts are affined each to a certain CPU.
The same portal interrupt services all the QMan portal consumers.
By default the DPAA Ethernet driver enables RSS, making use of the
DPAA FMan Parser and Keygen blocks to distribute traffic on 128
hardware frame queues using a hash on IP v4/v6 source and destination
and L4 source and destination ports, in present in the received frame.
When RSS is disabled, all traffic received by a certain interface is
received on the default Rx frame queue. The default DPAA Rx frame
queues are configured to put the received traffic into a pool channel
that allows any available CPU portal to dequeue the ingress traffic.
The default frame queues have the HOLDACTIVE option set, ensuring that
traffic bursts from a certain queue are serviced by the same CPU.
This ensures a very low rate of frame reordering. A drawback of this
is that only one CPU at a time can service the traffic received by a
certain interface when RSS is not enabled.
To implement RSS, the DPAA Ethernet driver allocates an extra set of
128 Rx frame queues that are configured to dedicated channels, in a
round-robin manner. The mapping of the frame queues to CPUs is now
hardcoded, there is no indirection table to move traffic for a certain
FQ (hash result) to another CPU. The ingress traffic arriving on one
of these frame queues will arrive at the same portal and will always
be processed by the same CPU. This ensures intra-flow order preservation
and workload distribution for multiple traffic flows.
RSS can be turned off for a certain interface using ethtool, i.e.
# ethtool -N fm1-mac9 rx-flow-hash tcp4 ""
To turn it back on, one needs to set rx-flow-hash for tcp4/6 or udp4/6:
# ethtool -N fm1-mac9 rx-flow-hash udp4 sfdn
There is no independent control for individual protocols, any command
run for one of tcp4|udp4|ah4|esp4|sctp4|tcp6|udp6|ah6|esp6|sctp6 is
going to control the rx-flow-hashing for all protocols on that interface.
Besides using the FMan Keygen computed hash for spreading traffic on the
128 Rx FQs, the DPAA Ethernet driver also sets the skb hash value when
the NETIF_F_RXHASH feature is on (active by default). This can be turned
on or off through ethtool, i.e.:
# ethtool -K fm1-mac9 rx-hashing off
# ethtool -k fm1-mac9 | grep hash
receive-hashing: off
# ethtool -K fm1-mac9 rx-hashing on
Actual changes:
receive-hashing: on
# ethtool -k fm1-mac9 | grep hash
receive-hashing: on
Please note that Rx hashing depends upon the rx-flow-hashing being on
for that interface - turning off rx-flow-hashing will also disable the
rx-hashing (without ethtool reporting it as off as that depends on the
NETIF_F_RXHASH feature flag).
Debugging
=========