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Solaris Dynamic Tracing Guide
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Document Information


1.  Introduction

2.  Types, Operators, and Expressions

3.  Variables

4.  D Program Structure

5.  Pointers and Arrays

6.  Strings

7.  Structs and Unions

8.  Type and Constant Definitions

9.  Aggregations

10.  Actions and Subroutines

11.  Buffers and Buffering

12.  Output Formatting

13.  Speculative Tracing

14.  dtrace(1M) Utility

15.  Scripting

16.  Options and Tunables

17.  dtrace Provider

18.  lockstat Provider


Adaptive Lock Probes

Spin Lock Probes

Thread Locks

Readers/Writer Lock Probes


19.  profile Provider

20.  fbt Provider

21.  syscall Provider

22.  sdt Provider

23.  sysinfo Provider

24.  vminfo Provider

25.  proc Provider

26.  sched Provider

27.  io Provider

28.  mib Provider

29.  fpuinfo Provider

30.  pid Provider

31.  plockstat Provider

32.  fasttrap Provider

33.  User Process Tracing

34.  Statically Defined Tracing for User Applications

35.  Security

36.  Anonymous Tracing

37.  Postmortem Tracing

38.  Performance Considerations

39.  Stability

40.  Translators

41.  Versioning



Spin Lock Probes

Threads cannot block in some contexts in the kernel, such as high-level interrupt context and any context manipulating dispatcher state. In these contexts, this restriction prevents the use of adaptive locks. Spin locks are instead used to effect mutual exclusion to critical sections in these contexts. As the name implies, the behavior of these locks in the presence of contention is to spin until the lock is released by the owning thread. The three probes pertaining to spin locks are in Table 18-2.

Table 18-2 Spin Lock Probes

Hold-event probe that fires immediately after a spin lock is acquired.
Contention-event probe that fires after a thread that has spun on a held spin lock has successfully acquired the spin lock. If both are enabled, spin-spin fires before spin-acquire. arg1 for spin-spin contains the spin time: the number of nanoseconds that were spent in the spin state before the lock was acquired. The spin count has little meaning on its own, but can be used to compare spin times.
Hold-event probe that fires immediately after a spin lock is released.

Adaptive locks are much more common than spin locks. The following script displays totals for both lock types to provide data to support this observation.

/execname == "date"/
    @locks["adaptive"] = count();

/execname == "date"/
    @locks["spin"] = count();

Run this script in one window, and a date(1) command in another. When you terminate the DTrace script, you will see output similar to the following example:

# dtrace -s ./whatlock.d
dtrace: script './whatlock.d' matched 5 probes 
spin                                                             26
adaptive                                                       2981

As this output indicates, over 99 percent of the locks acquired in running the date command are adaptive locks. It may be surprising that so many locks are acquired in doing something as simple as a date. The large number of locks is a natural artifact of the fine-grained locking required of an extremely scalable system like the Solaris kernel.