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Oracle® Solaris 11.4 DTrace (Dynamic Tracing) Guide

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Updated: September 2020
 
 

profile Provider

The profile provider provides probes associated with a time-based interrupt firing every fixed, specified time interval. These unanchored probes that are not associated with any particular point of execution, but rather with the asynchronous interrupt event. These probes can be used to sample some aspect of system state every unit time and the samples can then be used to infer system behavior. If the sampling rate is high, or the sampling time is long, an accurate inference is possible. Using DTrace actions, the profile provider can be used to sample practically anything in the system. For example, you could sample the state of the current thread, the state of the CPU, or the current system instruction.

profile-n Probes

A profile-n probe fires every fixed interval on every CPU at high interrupt level. The probe's firing interval is denoted by the value of n: the interrupt source will fire n times per second. n may also have an optional time suffix, in which case n is interpreted to be in the units denoted by the suffix. Figure 49, Table 49, Valid Time Suffixes for the profile Probe lists the valid suffixes and the units denoted by the suffix.

Table 49  Valid Time Suffixes for the profile Probe
Suffix
Time Units
nsec or ns
nanoseconds
usec or us
microseconds
msec or ms
milliseconds
sec or s
seconds
min or m
minutes
hour or h
hours
day or d
days
hz
hertz (frequency per second)
Example 28  Using a Profile Probe to Sample a Process

The following example creates a probe to fire at 97 hertz to sample the currently running process:

#pragma D option quiet

profile-97
/pid != 0/
{
        @proc[pid, execname] = count();
}

END
{
        printf("%-8s %-40s %s\n", "PID", "CMD", "COUNT");
        printa("%-8d %-40s %@d\n", @proc);
}

Running the preceding example for a brief period of time results in output similar to the following example:

# dtrace -s ./prof.d
^C
PID      CMD                                      COUNT
223887   sh                                       1
100360   httpd                                    1
100409   mibiisa                                  1
223887   uname                                    1
218848   sh                                       2
218984   adeptedit                                2
100224   nscd                                     3
3        fsflush                                  4
2        pageout                                  6
100372   java                                     7
115279   xterm                                    7
100460   Xsun                                     7
100475   perfbar                                  9
223888   prstat 															15

You can also use the profile-n provider to sample information about the running process. The following example D script uses a 1,001 hertz profile probe to sample the current priority of a specified process:

profile-1001
/pid == $1/
{
        @proc[execname] = lquantize(curlwpsinfo->pr_pri, 0, 100, 10);
}

To see this example script in action, type the following commands in one window:

$ echo $$
494621
$ while true ; do let i=0 ; done

In another window, run the D script for a brief period of time:

# dtrace -s ./profpri.d 494621
 dtrace: script './profpri.d' matched 1 probe
^C
ksh                                               
           value  ------------- Distribution ------------- count    
             < 0 |                                         0        
               0 |@@@@@@@@@@@@@@@@@@@@@                    7443     
              10 |@@@@@@                                   2235     
              20 |@@@@                                     1679     
              30 |@@@                                      1119     
              40 |@                                        560      
              50 |@                                        554      
              60 |                                         0 

This output shows the bias of the time-sharing scheduling class. Because the shell process is spinning on the CPU, its priority is constantly being lowered by the system. If the shell process were running less frequently, its priority would be higher. To see this result, type Control-C in the spinning shell and run the script again:

# dtrace -s ./profpri.d 494621
 dtrace: script './profpri.d' matched 1 probe

Type a few characters in the shell. When you terminate the DTrace script, output like the following example will appear:

ksh                                               
           value  ------------- Distribution ------------- count    
              40 |                                         0        
              50 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 14       
              60 |                                         0

Because the shell process was sleeping awaiting user input instead of spinning on the CPU, when it did run it was run at a much higher priority.

tick-n Probes

Like profile-n probes, tick-n probes fire every fixed interval at high interrupt level. However, unlike profile-n probes, which fire on every CPU, tick- n probes fire on only one CPU per interval. The actual CPU may change over time. As with profile-n probes, n defaults to rate-per-second but might also have an optional time suffix. tick-n probes have several uses, such as providing some periodic output or taking a periodic action.

profile Probe Arguments

The arguments to the profile probes are as follows:

Argument
Description
arg0
The program counter (PC) in the kernel at the time that the probe fired, or 0 if the current process was not executing in the kernel at the time that the probe fired.
arg1
The PC in the user-level process at the time that the probe fired, or 0 if the current process was executing at the kernel at the time that the probe fired.

As the descriptions imply, if arg0 is non-zero then arg1 is zero; if arg0 is zero then arg1 is non-zero. Thus, you can use arg0 and arg1 to differentiate user-level from kernel level, as in this example:

profile-1ms
{
        @ticks[arg0 ? "kernel" : "user"] = count();
}

profile Timer Resolution

The profile provider uses arbitrary resolution interval timers in the operating system. On architectures that do not support arbitrary resolution time-based interrupts, the frequency is limited by the system clock frequency, which is specified by the hz kernel variable. Probes of higher frequency than hz on such architectures will fire some number of times every 1/hz seconds. For example, a 1000 hertz profile probe on such an architecture with hz set to 100 would fire ten times in rapid succession every ten milliseconds. On platforms that support arbitrary resolution, a 1000 hertz profile probe would fire exactly every one millisecond.

Example 29  Reporting Platform Resolution From the Profile Probe

The following example tests a given architecture's resolution:

profile-5000
{
        /*
         * Divide by 1,000,000 to convert nanoseconds to milliseconds, and
         * then take the value mod 10 to get the current millisecond within
         * a 10 millisecond window.  On platforms that do not support truly
         * arbitrary resolution profile probes, all of the profile-5000 probes
         * will fire on roughly the same millisecond.  On platforms that
         * support a truly arbitrary resolution, the probe firings will be
         * evenly distributed across the milliseconds.
         */
        @ms = lquantize((timestamp / 1000000) % 10, 0, 10, 1);
}

tick-1sec
/i++ >= 10/
{
        exit(0);
}

On an architecture that supports arbitrary resolution profile probes, running the example script will yield an even distribution:

# dtrace -s ./restest.d
 dtrace: script './restest.d' matched 2 probes
CPU     ID                    FUNCTION:NAME
  0  33631                       :tick-1sec 
           value  ------------- Distribution ------------- count    
             < 0 |                                         0        
               0 |@@@                                      10760    
               1 |@@@@                                     10842    
               2 |@@@@                                     10861    
               3 |@@@                                      10820    
               4 |@@@                                      10819    
               5 |@@@                                      10817    
               6 |@@@@                                     10826    
               7 |@@@@                                     10847    
               8 |@@@@                                     10830    
               9 |@@@@                                     10830

On an architecture that does not support arbitrary resolution profile probes, running the example script will yield an uneven distribution:

# dtrace -s ./restest.d
 dtrace: script './restest.d' matched 2 probes
 CPU     ID                    FUNCTION:NAME
  0  28321                       :tick-1sec 
           value  ------------- Distribution ------------- count    
               4 |                                         0        
               5 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@  107864   
               6 |                                         424      
               7 |                                         255      
               8 |                                         496      
               9 |                                         0

On these architectures, hz may be manually tuned in /etc/system to improve the effective profile resolution.

Currently, all variants of UltraSPARC (sun4v) support arbitrary resolution profile probes. Many variants of the x86 architecture (i86pc) also support arbitrary resolution profile probes, although some older variants do not support arbitrary resolution profile probes.

profile Probe Creation

Unlike other providers, the profile provider creates probes dynamically based on the requirement. Thus, the desired profile probe might not appear in a listing of all probes but the probe will be created when it is explicitly enabled. You can use the dtrace -l -P profile to list all the probes.

On architectures that support arbitrary resolution profile probes, a time interval that is too short causes the system to continuously field time-based interrupts, thereby denying service on the system. To prevent this situation, the profile provider silently refuses to create any probe that would result in an interval of less than two hundred microseconds.

profile Stability

The profile provider uses stability mechanism of DTrace to describe its stabilities as shown in the following table. For more information about the stability mechanism, see DTrace Stability Mechanisms.

Table 50  Stability Mechanism for the profile Provider
Element
Name Stability
Data Stability
Dependency Class
Provider
Evolving
Evolving
Common
Module
Unstable
Unstable
Unknown
Function
Private
Private
Unknown
Name
Evolving
Evolving
Common
Arguments
Evolving
Evolving
Common