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26b67f5a1e
i210 has a total of 24KB of transmit packet buffer. When in Qav mode,
this buffer is divided into four pieces, one for each Tx queue.
Currently, 8KB are given to each of the two SR queues and 4KB are given
to each of the two SP queues.
However, it was noticed that such distribution can make best effort
traffic (which would usually go to the SP queues when Qav is enabled, as
the SR queues would be used by ETF or CBS qdiscs for TSN-aware traffic)
perform poorly. Using iperf3 to measure, one could see the performance
of best effort traffic drop by nearly a third (from 935Mbps to 578Mbps),
with no TSN traffic competing.
This patch redistributes the 24KB to each queue equally: 6KB each. On
tests, there was no notable performance reduction of best effort traffic
performance when there was no TSN traffic competing.
Below, more details about the data collected:
All experiments were run using the following qdisc setup:
qdisc taprio 100: root refcnt 9 tc 4 map 3 3 3 2 3 0 0 3 3 3 3 3 3 3 3 3
queues offset 0 count 1 offset 1 count 1 offset 2 count 1 offset 3 count 1
clockid TAI base-time 0 cycle-time 10000000 cycle-time-extension 0
index 0 cmd S gatemask 0xf interval 10000000
qdisc etf 8045: parent 100:1 clockid TAI delta 1000000 offload on
deadline_mode off skip_sock_check off
TSN traffic, when enabled, had this characteristics:
Packet size: 1500 bytes
Transmission interval: 125us
----------------------------------
Without this patch:
----------------------------------
- TCP data:
- No TSN traffic:
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-20.00 sec 1.35 GBytes 578 Mbits/sec 0
- With TSN traffic:
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-20.00 sec 1.07 GBytes 460 Mbits/sec 1
- TCP data limiting iperf3 buffer size to 4K:
- No TSN traffic:
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-20.00 sec 1.35 GBytes 579 Mbits/sec 0
- With TSN traffic:
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-20.00 sec 1.08 GBytes 462 Mbits/sec 0
- TCP data limiting iperf3 buffer size to 192 bytes (smallest size without
serious performance degradation):
- No TSN traffic:
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-20.00 sec 1.34 GBytes 577 Mbits/sec 0
- With TSN traffic:
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-20.00 sec 1.07 GBytes 461 Mbits/sec 1
- UDP data at 1000Mbit/sec:
- No TSN traffic:
[ ID] Interval Transfer Bitrate Jitter Lost/Total Datagrams
[ 5] 0.00-20.00 sec 1.36 GBytes 586 Mbits/sec 0.000 ms 0/1011407 (0%)
- With TSN traffic:
[ ID] Interval Transfer Bitrate Jitter Lost/Total Datagrams
[ 5] 0.00-20.00 sec 1.05 GBytes 451 Mbits/sec 0.000 ms 0/778672 (0%)
----------------------------------
With this patch:
----------------------------------
- TCP data:
- No TSN traffic:
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-20.00 sec 2.17 GBytes 932 Mbits/sec 0
- With TSN traffic:
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-20.00 sec 1.50 GBytes 646 Mbits/sec 1
- TCP data limiting iperf3 buffer size to 4K:
- No TSN traffic:
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-20.00 sec 2.17 GBytes 931 Mbits/sec 0
- With TSN traffic:
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-20.00 sec 1.50 GBytes 645 Mbits/sec 0
- TCP data limiting iperf3 buffer size to 192 bytes (smallest size without
serious performance degradation):
- No TSN traffic:
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-20.00 sec 2.17 GBytes 932 Mbits/sec 1
- With TSN traffic:
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-20.00 sec 1.50 GBytes 645 Mbits/sec 0
- UDP data at 1000Mbit/sec:
- No TSN traffic:
[ ID] Interval Transfer Bitrate Jitter Lost/Total Datagrams
[ 5] 0.00-20.00 sec 2.23 GBytes 956 Mbits/sec 0.000 ms 0/1650226 (0%)
- With TSN traffic:
[ ID] Interval Transfer Bitrate Jitter Lost/Total Datagrams
[ 5] 0.00-20.00 sec 1.51 GBytes 649 Mbits/sec 0.000 ms 0/1120264 (0%)
Signed-off-by: Ederson de Souza <ederson.desouza@intel.com>
Tested-by: Tony Brelinski <tonyx.brelinski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.