Document ts2phc offset spike mitigation and new parameter (dsr8mr3)
Change-Id: I88b65a84f8f879d716e37fb2e9e6b67a74e793ac Signed-off-by: Ngairangbam Mili <ngairangbam.mili@windriver.com>
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Ngairangbam Mili
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@ -75,7 +75,7 @@ Each of the fields are explained below:
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parameter.
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.. code-block:: none
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~(keystone_admin)]$ system ptp-instance-parameter-add <ptp4l instance> clockAccuracy=0x21
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@ -205,3 +205,139 @@ The |PTP| Announce Message Attributes can be viewed using the `pmc` tool.
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The log output for dynamically updated values can be found in
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``/var/log/collectd.log``.
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Ts2phc Offset Spike Mitigation
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------------------------------
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Ts2phc can be configured to detect and ignore intermittent offset spikes that
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may result in incorrect clock adjustments. This behaviour is controlled using
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the global instance parameter ``max_phc_update_skip_cnt``. The
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``max_phc_update_skip_cnt`` parameter is the number of consecutive offset
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spikes in a row that will be ignored. For example, setting
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``max_phc_update_skip_cnt`` to 120 would allow ts2phc to ignore 120 consecutive
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offset spike incidents before adjusting the clock.
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Offset Spike Characterization
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The |prod| systems using the realtime kernel may experience an intermittent
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offset spike behaviour in ts2phc. This intermittent offset spike behaviour
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results from |GNSS| messages that take time to arrive at the userspace ts2phc
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application. The delayed |GNSS| messages can cause ts2phc application to
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calculate an incorrect adjustment value for the |PHCs|. This results in ts2phc
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making large adjustments to its |PHCs| and can cause unstable system time. An
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example of this behaviour can be seen in the log snippet below. If log events
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similar to the given example are observed, configuring offset spike mitigation
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in ts2phc can improve timing stability by detecting and ignoring these large
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offset calculations.
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Example:
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.. code-block:: none
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2024-03-07T15:39:57.821 controller-1 ts2phc: debug [212517.301] ts11 nmea sentence: GNRMC
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2024-03-07T15:39:58.001 controller-1 ts2phc: debug [212517.480] ts11 nmea delay: 820982637 ns
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### Large nmea delay value above ^^ indicates an offset spike has occurred
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2024-03-07T15:39:58.001 controller-1 ts2phc: debug [212517.480] ts11 enp81s0f1 extts index 0 at 1709826035.000000000 corr 0 src 1709826034.179042651 diff 1000000000 servo state 2
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2024-03-07T15:39:58.001 controller-1 ts2phc: debug [212517.480] ts11 enp81s0f1 master offset1000000000 s2 freq +900000000
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### Ts2phc makes large adjustment ^^ to clock, resulting in degraded timing accuracy
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2024-03-07T15:39:58.058 controller-1 ts2phc: debug [212517.538] ts11 nmea sentence: GNRMC
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2024-03-07T15:39:58.935 controller-1 ts2phc: debug [212518.413] ts11 nmea delay: 58600490 ns
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2024-03-07T15:39:58.935 controller-1 ts2phc: debug [212518.413] ts11 enp81s0f1 extts index 0 at 1709826035.100878397 corr 0 src 1709826036.874841070 diff -899121603 servo state 2
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2024-03-07T15:39:58.935 controller-1 ts2phc: debug [212518.413] ts11 enp81s0f1 master offset -899121603 s2 freq -899121603
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### Subsequent cycles show wide swings ^^ in clock adjustments as ts2phc stabilizes
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2024-03-07T15:39:58.999 controller-1 ts2phc: debug [212518.479] ts11 nmea sentence: GNRMC
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2024-03-07T15:39:59.834 controller-1 ts2phc: debug [212519.313] ts11 nmea delay: -449462 ns
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2024-03-07T15:39:59.834 controller-1 ts2phc: debug [212519.313] ts11 enp81s0f1 extts index 0 at 1709826036.996688203 corr 0 src 1709826037.833824291 diff -3311797 servo state 2
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2024-03-07T15:39:59.834 controller-1 ts2phc: debug [212519.313] ts11 enp81s0f1 master offset -3311797 s2 freq -273048278
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2024-03-07T15:40:04.178 controller-1 ts2phc: debug [212523.658] ts11 nmea sentence: GNRMC [… omitted lines]
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2024-03-07T15:40:32.054 controller-1 ts2phc: debug [212551.534] ts11 nmea sentence: GNRMC
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2024-03-07T15:40:33.000 controller-1 ts2phc: debug [212552.480] ts11 nmea delay: 54715299 ns
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2024-03-07T15:40:33.000 controller-1 ts2phc: debug [212552.480] ts11 enp81s0f1 extts index 0 at 1709826070.000000003 corr 0 src 1709826070.945357401 diff 3 servo state 2
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2024-03-07T15:40:33.000 controller-1 ts2phc: debug [212552.480] ts11 enp81s0f1 master offset 3 s2 freq +2
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2024-03-07T15:40:33.054 controller-1 ts2phc: debug [212552.534] ts11 nmea sentence: GNRMC
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2024-03-07T15:40:34.002 controller-1 ts2phc: debug [212553.480] ts11 nmea delay: 54504252 ns
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2024-03-07T15:40:34.002 controller-1 ts2phc: debug [212553.480] ts11 enp81s0f1 extts index 0 at 1709826071.000000001 corr 0 src 1709826071.945587288 diff 1 servo state 2
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2024-03-07T15:40:34.002 controller-1 ts2phc: debug [212553.480] ts11 enp81s0f1 master offset 1 s2 freq +0
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### After a period of 25-30 seconds, ts2phc has stabilized and is back to small adjustments
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Configure Offset Spike Mitigation
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The offset spike mitigation behaviour is enabled in ts2phc by default with a
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value of ``max_phc_update_skip_cnt`` = 120.
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To configure the number of consecutive offset spikes that will be ignored by ts2phc, use the
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following |PTP| instance parameter:
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.. code-block:: none
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system ptp-instance-parameter-add <ts2phc instance name> max_phc_update_skip_cnt=120
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# Apply the configuration. This will restart all PTP services.
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system ptp-instance-apply
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The value 120 will allow ts2phc to ignore up to 120 consecutive offset spikes.
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This value may need to be adjusted based on testing and observation in your environment.
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Consecutive occurrences are not observed often, with subsequent updates
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arriving in a timely manner.
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Disable Offset Spike Mitigation
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The offset spike mitigation can be disabled by setting ``max_phc_update_skip_cnt=0``.
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**Offset mitigation log example:**
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.. code-block:: none
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2024-03-07T15:41:04.639 controller-1 ts2phc: debug [212584.120] ts11 nmea sentence: GNRMC
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2024-03-07T15:41:05.013 controller-1 ts2phc: debug [212584.493] ts11 nmea delay: 639834481 ns
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### Large nmea delay above ^^ indicating an offset spike has occurred
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2024-03-07T15:41:05.013 controller-1 ts2phc: debug [212584.493] ts11 enp81s0f1 extts index 0 at 1709826102.000000000 corr 0 src 1709826101.373785045 diff 1000000000 servo state 2
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2024-03-07T15:41:05.013 controller-1 ts2phc: debug [212584.493] ts11 Offset spike detected. Skip current PHC update enp81s0f1 offset 1000000000 s2 freq +0
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### Mitigation catches this and skips adjusting the clock ^^
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2024-03-07T15:41:05.013 controller-1 ts2phc: debug [212584.493] ts11 Current skip count: 1
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### “Current skip count” ^^ indicates the number of consecutive spikes detected
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### Because the next update to arrive does not have an offset spike, the current skip count will be reset to 0 and will begin incrementing again when another spike occurs
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2024-03-07T15:41:05.063 controller-1 ts2phc: debug [212584.543] ts11 nmea sentence: GNRMC
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2024-03-07T15:41:06.001 controller-1 ts2phc: debug [212585.480] ts11 nmea delay: 63592544 ns
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2024-03-07T15:41:06.001 controller-1 ts2phc: debug [212585.480] ts11 enp81s0f1 extts index 0 at 1709826103.000000000 corr 0 src 1709826103.936434314 diff 0 servo state 2
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2024-03-07T15:41:06.001 controller-1 ts2phc: debug [212585.480] ts11 enp81s0f1 master offset 0 s2 freq +0
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### Subsequent ts2phc adjustments are small because the clock remained tightly synced
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2024-03-07T15:41:06.067 controller-1 ts2phc: debug [212585.533] ts11 nmea sentence: GNRMC
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2024-03-07T15:41:07.000 controller-1 ts2phc: debug [212586.480] ts11 nmea delay: 53524772 ns
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2024-03-07T15:41:07.000 controller-1 ts2phc: debug [212586.480] ts11 enp81s0f1 extts index 0 at 1709826104.000000000 corr 0 src 1709826104.946499286 diff 0 servo state 2
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2024-03-07T15:41:07.000 controller-1 ts2phc: debug [212586.480] ts11 enp81s0f1 master offset 0 s2 freq +0
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2024-03-07T15:41:07.050 controller-1 ts2phc: debug [212586.530] ts11 nmea sentence: GNRMC
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2024-03-07T15:41:08.000 controller-1 ts2phc: debug [212587.480] ts11 nmea delay: 50802510 ns
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2024-03-07T15:41:08.000 controller-1 ts2phc: debug [212587.480] ts11 enp81s0f1 extts index 0 at 1709826104.999999999 corr 0 src 1709826105.949221716 diff -1 servo state 2
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2024-03-07T15:41:08.000 controller-1 ts2phc: debug [212587.480] ts11 enp81s0f1 master offset -1 s2 freq -1
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**Ts2phc config file example:**
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.. code-block::
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[global]
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##
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## Default Data Set
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##
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leapfile /usr/share/zoneinfo/leap-seconds.list
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message_tag ts11
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ts2phc.nmea_serialport /dev/ttyGNSS_5100_0
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ts2phc.pulsewidth 100000000
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logging_level 7
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max_phc_update_skip_cnt 120
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[enp81s0f1]
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##
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## Associated interface: enp81s0f1
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##
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ts2phc.extts_polarity rising
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