System and method for measuring latch contention

• US 20050203904A1
• Filed: 03/11/2004
• Published: 09/15/2005
• Est. Priority Date: 03/11/2004
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Van Fleet, James William, Mehaffy, David William
• Granted Patent: US 7,318,220 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06F 9/526 Mutual exclusion algorithms
• CPC Class Codes: Y10S 707/99938 Concurrency, e.g. lock management in shared database

Abstract

A system and method is provided for measuring lock usage in a non-intrusive manner. Measurements are performed only when a lock is contended. When a lock is requested and the lock is available (i.e., is not contended), the only data gathered is a counter that is incremented to keep track of the number of times the particular lock was requested. When a lock is contended, an operating system trace hook is requested. The trace hook records data such as the timestamp that the requestor requested the lock, the request count, a stack traceback to identify the function corresponding to the requestor, and the address of the lock that was requested. Post-operative processing analyzes the recorded trace hook data to identify contended locks and processes that may not be efficiently using locks.

Claims

1. A computer implemented method comprising:

receiving requests for a shared resource, wherein access to the shared resource is controlled with a software lock;

detecting that the software lock is unavailable;

emitting an operating system trace hook in response to the detecting, wherein the operating system trace hook is adapted to record lock usage data; and

analyzing the recorded lock usage data.

2. The method of claim 1 wherein the lock usage data includes a timestamp corresponding to each request, a lock address corresponding to an address of the software lock, a stack call chain for each process making one of the requests at the time the corresponding request was made, and a request count.

3. The method of claim 1 further comprising:

receiving a lock release request from a process that currently holds the software lock;

determining whether other processes are currently waiting for the software lock;

emitting a second operating system trace hook and releasing the software lock in response to determining that other processes are currently waiting for the software lock, wherein the second operating system trace hook is also adapted to record lock usage data; and

releasing the software lock without emitting a trace hook in response to determining that other processes are not waiting for the software lock.

4. The method of claim 1 further comprising:

identifying one or more processes causing lock contention in response to the analysis of the lock usage data.

5. The method of claim 4 further comprising:

modifying the identified processes'"'"' usage of the shared resource.

6. The method of claim 1 further comprising:

detecting that the software lock is available in response to receiving the request;

incrementing a lock counter that tracks the number of times the shared resource was requested; and

setting ownership of the software lock to an identifier corresponding to an identifier of the requesting process.

7. The method of claim 6 wherein the setting ownership further includes:

requesting that a lock ownership field of the software lock be set to the requesting process identifier; and

receiving a completion code indicating that the ownership has been set, wherein the incrementing of the lock counter is performed in parallel with the setting ownership by incrementing the lock counter after the request for the lock ownership field has been set and before the completion code has been received.

20. The computer program product of claim 6 wherein the means for setting ownership further includes:

means for requesting that a lock ownership field of the software lock be set to the requesting process identifier; and

means for receiving a completion code indicating that the ownership has been set, wherein the means for incrementing the lock counter is performed in parallel with the means for setting ownership by incrementing the lock counter after the request for the lock ownership field has been set and before the completion code has been received.

8. An information handling system comprising:

one or more processors;

a memory accessible by the processors;

one or more shared resources accessible by the processors;

a nonvolatile storage device accessible by the processors;

one or more software locks, stored in the memory, for controlling access to the shared resources;

an operating system that controls a plurality of processes performed by the processors, the operating system including a trace hook facility; and

a software lock measurement tool for measuring lock contention, the software lock measurement tool including;

means for receiving requests from one or more of the processes for one of the shared resources, wherein access to the shared resource is controlled with one of the software locks;

means for detecting that the software lock is unavailable;

means for emitting an operating system trace hook in response to the detecting, wherein the

operating system trace hook is adapted to record lock usage data; and

means for analyzing the recorded lock usage data.

9. The information handling system of claim 8 wherein the lock usage data includes a timestamp corresponding to each request, a lock address corresponding to an address of the software lock, a stack call chain for each process making one of the requests at the time the corresponding request was made, and a request count.

10. The information handling system of claim 8 further comprising:

means for receiving a lock release request from a process that currently holds the software lock;

means for determining whether other processes are currently waiting for the software lock;

means for emitting a second operating system trace hook and releasing the software lock in response to determining that other processes are currently waiting for the software lock, wherein the second operating system trace hook is also adapted to record lock usage data; and

means for releasing the software lock without emitting a trace hook in response to determining that other processes are not waiting for the software lock.

11. The information handling system of claim 8 further comprising:

means for identifying one or more processes causing lock contention in response to the analysis of the lock usage data.

12. The information handling system of claim 8 further comprising:

means for detecting that the software lock is available in response to receiving the request;

means for incrementing a lock counter that tracks the number of times the shared resource was requested; and

means for setting ownership of the software lock to an identifier corresponding to an identifier of the requesting process.

13. The information handling system of claim 12 wherein the means for setting ownership further includes:

means for requesting that a lock ownership field of the software lock be set to the requesting process identifier; and

means for receiving a completion code indicating that the ownership has been set, wherein the means for incrementing the lock counter is performed in parallel with the means for setting ownership by incrementing the lock counter after the request for the lock ownership field has been set and before the completion code has been received.

14. A computer program product stored on a computer operable media for measuring lock contention, said computer program product comprising:

means for receiving requests for a shared resource, wherein access to the shared resource is controlled with a software lock;

means for detecting that the software lock is unavailable;

means for emitting an operating system trace hook in response to the detecting, wherein the operating system trace hook is adapted to record lock usage data; and

means for analyzing the recorded lock usage data.

15. The computer program product of claim 14 wherein the lock usage data includes a timestamp corresponding to each request, a lock address corresponding to an address of the software lock, a stack call chain for each process making one of the requests at the time the corresponding request was made, and a request count.

16. The computer program product of claim 14 further comprising:

means for receiving a lock release request from a process that currently holds the software lock;

means for determining whether other processes are currently waiting for the software lock;

means for emitting a second operating system trace hook and releasing the software lock in response to determining that other processes are currently waiting for the software lock, wherein the second operating system trace hook is also adapted to record lock usage data; and

means for releasing the software lock without emitting a trace hook in response to determining that other processes are not waiting for the software lock.

17. The computer program product of claim 14 further comprising:

means for identifying one or more processes causing lock contention in response to the analysis of the lock usage data.

18. The computer program product of claim 17 further comprising:

means for modifying the identified processes'"'"' usage of the shared resource.

19. The computer program product of claim 14 further comprising:

means for detecting that the software lock is available in response to receiving the request;

means for incrementing a lock counter that tracks the number of times the shared resource was requested; and

means for setting ownership of the software lock to an identifier corresponding to an identifier of the requesting process.