Multinode computer system with distributed clock synchronization system

• US 6,591,370 B1
• Filed: 12/23/1999
• Issued: 07/08/2003
• Est. Priority Date: 12/23/1999
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Gilbert, Bruce M., Lovett, Thomas D., Berg, Thomas B.
• Primary Examiner(s): Lee, Thomas
• Assistant Examiner(s): CONNOLLY, MARK A
• Application Number:
  US09/471,939
• Time in Patent Office: 1,293 Days
• Field of Search: 713/500, 713/502, 327/153, 327/151
• US Class Current: 713/502
• CPC Class Codes: G06F 1/14 Time supervision arrangements, e.g. real time clock
• CPC Class Codes: H03L 7/00 Automatic control of frequency or phase; Synchronisation

Abstract

A multinode multiprocessor computer system with distributed local clocks wherein a local clock may be synchronized with other clocks in the system without affecting the operation of the other clocks. A local clock to be synchronized is reset and counts an elapsed time since the reset. Simultaneously with resetting the local clock, a clock value from a clock on a source node is stored. The clock value from the source node is copied to the node to be synchronized and added to the elapsed time. The resulting summation is then stored in the local clock to be synchronized. As a result, the local clock is synchronized to the clock on the source node. In one system embodiment, the local clock includes a dynamic register and a base register and an adder adds the two portions together to generate an output of the local clock. For a node being synchronized, the dynamic portion is reset and allowed to count the elapsed time while the base portion is loaded with a clock value copied from the source node. In another system embodiment, a clock register stores both dynamic and base portions. For a node being synchronized, the clock register is reset and allowed to count the elapsed time. The base portion from the source node is then added to the clock register and stored in the clock register.

Claims

1. In a multinode multiprocessor computer system having distributed associated local clocks on the nodes, a method of synchronizing the associated local clocks on at least two of the nodes, comprising:

in response to a synchronization signal asserted on a system-wide synchronization line, counting a respective elapsed time on each of the nodes to be synchronized;

storing a clock value from a first node, the clock value representing a current time of a local clock on the first node; and

adding the clock value from the first node to the respective elapsed time counted on the each of the nodes to be synchronized individually, thereby obtaining a local clock value for the associated local clock on the each of the nodes to be synchronized.

2. The method of claim 1, wherein the local clock on the second node is continuously running during synchronization of the local clock of the first node.

3. The method of claim 1, further including providing a base register on the first node and storing the clock value from the second node in the base register.

4. The method of claim 3, further including providing a dynamic register on the first node, wherein the elapsed time is stored in the dynamic register, and the local clock value for the first node is obtained by adding the clock value in the base register to the elapsed time in the dynamic register.

5. The method of claim 1, further including storing the synchronized local clock value in a register in the first node.

6. The method of claim 1, further including controlling the counting of the elapsed time on the first node with a system clock to which the first node is coupled without any intermediating nodes.

7. The method of claim 1, wherein storing the clock value from the second node occurs in response to a change in the synchronization signal.

8. The method of claim 1, wherein the elapsed time starts from the activation or deactivation of the synchronization signal.

9. The method of claim 1, further including providing a counter that is cleared in response to the synchronization signal, the counter for counting the elapsed time.

10. The method of claim 1, wherein the storing of the clock value and a start of the counting of the elapsed time occur substantially simultaneously.

11. The method of claim 1, wherein each node includes at least a processor and a local clock.

12. In a multinode computer system having distributed local clocks on the nodes, a method of synchronizing an associated local clock on at least two of the nodes, comprising:

counting an elapsed time on each of the nodes having a local clock to be synchronized after receiving a signal on a system-wide synchronize line, the elapsed time stored in a dynamic register of the node;

reading a clock value from a clock of a first node in the multinode computer system that is not located on the at least two nodes to be synchronized, the clock value stored in a base register of the first node; and

adding the clock value from the clock to the elapsed time counted on each of the nodes to be synchronized respectively using an adder, to directly obtain a synchronized local clock value for each one of the at least two nodes to be synchronized.

13. The method of claim 12 further including providing a synchronization line coupled to the node and activating the synchronization line for starting the counting of the elapsed time.

14. The method of claim 12, further including providing the dynamic register coupled to a system clock and clearing the dynamic register in response to the activation of the synchronization line.

15. The method of claim 13, wherein the clock value read is from a local clock on a second node and further including providing a base register on the second node coupled to the synchronization line, the base register loading the clock value of the second node in response to activation of the synchronization line.

16. The method of claim 12 further including providing a system clock coupled to the local clocks on the nodes that increments the local clocks.

17. The method of claim 12, further including providing the dynamic register coupled to a system clock and wherein counting includes incrementing the dynamic register in response to the system clock.

18. The method of claim 12 including storing the added clock value in a single register that is the local clock and that provides the synchronized local clock value.

19. In a multinode computer system, a method of synchronizing a local clock on a node to other nodes in the system, comprising:

providing a local clock for each node in the multinode computer system, wherein the local clocks are running and synchronized with each other;

dynamically adding a node to the multinode computer system, wherein the dynamically added node includes a local clock that is not synchronized to the other local clocks in the multinode computer system;

reading a local clock value from a local clock on one of the nodes in the system other than the dynamically added node;

resetting a local clock on the dynamically added node and running the local clock after it is reset; and

adding the read clock value to a value in the local clock of the dynamically added node to synchronize the local clock on the dynamically added node.

20. The multinode computer system of claim 19, wherein the local clock on the dynamically added node has a dynamic portion and a base portion.

21. The multinode computer system of claim 19, wherein reading the local clock is accomplished without affecting the local clock.

22. The multinode computer system of claim 19, further including activating a synchronize line that simultaneously causes the reading and the resetting.

23. The multinode computer system of claim 19, further including:

enabling a clear signal to the dynamically added node to clear its local clock; and

disabling a clear signal to all nodes other than the dynamically added node so that the local clocks are not cleared on the other nodes.

24. The multinode computer system of claim 19, wherein the local clock includes a base portion and a dynamic portion and further including activating a synchronize signal that adds the base portion to the dynamic portion and storing the added value in the base register.

25. A clock synchronization system, comprising:

multiple nodes, each with an associated local clock on the node, wherein at least two of the local clocks are to be synchronized with another one of the local clocks from one of the nodes;

each associated local clock including;

(a) a system-wide synchronize line that is activated to synchronize more than one of the associated local clocks to a local clock on another node;

(b) at least one clock register coupled to the synchronize line, the clock register storing an elapsed time that occurs since activation of the synchronize line for the associated local clock being synchronized; and

,

(c) an adder coupled to the at least one clock register, the adder adding contents of the at least one clock register with contents of at least one clock register on the one of the nodes to directly yield a value of the local clock.

26. The clock synchronization system of claim 25, further including a base register coupled to the clock register and the synchronization line that stores a current value of the clock register when the synchronization line is activated.

27. The clock synchronization system of claim 25, wherein a local clock includes a dynamic portion and a base portion and the clock register stores only the dynamic portion.

28. The clock synchronization system of claim 25, wherein a local clock includes a dynamic portion and a base portion.

29. The clock synchronization system of claim 25, further including a base register coupled to the clock register for storing a time value of the local clock in response to activation of the synchronize line.

30. The clock synchronization system of claim 29, wherein the base register stores a static portion of the time value of the local clock and in response to the activation of the synchronize line the base register stores the sum of the base register plus the clock register.

31. The clock synchronization system of claim 29, wherein in response to the activation of the synchronize line the value of the local clock is copied to the base register.

32. The clock synchronization system of claim 25 further including a global clock that the local clocks are synchronized to.

33. A multinode computer system having multiple nodes each with an associated local clock on the node, wherein at least two of the local clocks are to be synchronized with another one of the local clocks from one of the nodes, including a system clock wherein each node is coupled to the system clock without any intermediating nodes and includes at least one processor and a local clock having a dynamic register and a base register, a local clock operating in a first mode of operation wherein the dynamic register of the local clock is incremented in response to the system clock and a second mode of operation wherein a local clock is synchronized by writing a value to the base register of the local clock and resetting the dynamic register of the local clock, the local clock having a local clock value directly determined by adding a value of the base register and a value of the dynamic register, wherein the value of the dynamic register is affected by a signal received from a system-wide synchronize line.