Precision Time Protocol on Linux
[Pages:49]Precision Time Protocol on Linux ~ Introduction to linuxptp
Ken ICHIKAWA FUJITSU LIMITED. LinuxCon Japan 2014
Copyright 2014 FUJITSU LIMITED
Agenda
Background Overview of Precision Time Protocol (PTP) About PTP on Linux Tips For easy trial or development
3
Copyright 2014 FUJITSU LIMITED
Background
Event ordering is very important
for incident analysis, performance analysis and so on
Event ordering is based on timestamps
Timestamps are collected from multiple servers
Clock synchronization is important
If precision and accuracy of clock synchronization are bad, event ordering can reverse against actual time
Event 2
Event 1
Event 3
4
Server A
Server B
Copyright 2014 FUJITSU LIMITED
NTP is not enough
NTP provides millisecond level synchronization
Maybe enough for remote machines, but not enough for locally cooperating machines
Many events occur in a millisecond in multiple servers Event ordering will frequently reverse
Need another protocol
Higher precision and accuracy Not need to synchronize large area, but local servers
and devices
5
Copyright 2014 FUJITSU LIMITED
Example of wrong event ordering
Actual Time 2
3
4
5
6
7
8
Server A
diff:-1
1
Server B
diff:+3
5
2
3
Event 1
6
7
4
5
Event 2
8
9
6
7
Event 3
10
11
time
Event Ordering based on Actual Time
Time
Event
3
Event 1
5
Event 2
7
Event 3
Event Ordering based on Timestamp
Time
Event
2
Event 1
6
Event 3
reverse!
8
Event 2
6
Copyright 2014 FUJITSU LIMITED
Example of correct event ordering based on better clock synchronization
Actual Time 2
3
4
5
6
7
8
Server A diff:-0.001 1.999
2.999 3.999 Event 1
4.999 5.999 Event 2
6.999 7.999 Event 3
Server B diff:+0.003 2.003 3.003 4.003 5.003 6.003 7.003 8.003 time
Event Ordering based on Actual Time
Time
Event
3
Event 1
5
Event 2
7
Event 3
Event Ordering based on Timestamp
Time
Event
2.999
Event 1
5.003 6.999
Event 2 Event 3
correct!
7
Copyright 2014 FUJITSU LIMITED
Agenda
Background Overview of Precision Time Protocol (PTP)
What's PTP Term explanation About packet timestamp
About PTP on Linux Tips For easy trial or development
8
Copyright 2014 FUJITSU LIMITED
Precision Time Protocol (PTP)
Standardized protocol, IEEE1588 Synchronize the clocks in local computing systems
and devices Microsecond to sub-microsecond accuracy and
precision Administration free
Capability to autonomously decide time server(master)
? called Best Master Clock Algorithm (BMCA)
9
Copyright 2014 FUJITSU LIMITED
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