Arguments

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The arguments to sysinfo probes are as follows:

`arg0`	The value by which the statistic is to be incremented. For most probes, this argument is always 1, but for some probes this argument may take other values.
`arg1`	A pointer to the current value of the statistic to be incremented. This value is a 64–bit quantity that will be incremented by the value in arg0. Dereferencing this pointer enables consumers to determine the current count of the statistic corresponding to the probe.
`arg2`	A pointer to the `cpu_t` structure that corresponds to the CPU on which the statistic is to be incremented. This structure is defined in `<sys/cpuvar.h>`, but it is part of the kernel implementation and should be considered Private.

The value of arg0 is 1 for most sysinfo probes. However, the readch and writech probes set arg0 to the number of bytes read or written, respectively. This features permits you to determine the size of reads by executable name, as shown in the following example:

# dtrace -n readch'{@[execname] = quantize(arg0)}'
dtrace: description 'readch' matched 4 probes
^C
  xclock                                            
           value  ------------- Distribution ------------- count    
              16 |                                         0        
              32 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 1        
              64 |                                         0        

  acroread                                          
           value  ------------- Distribution ------------- count    
              16 |                                         0        
              32 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 3        
              64 |                                         0        

  FvwmAuto                                          
           value  ------------- Distribution ------------- count    
               2 |                                         0        
               4 |@@@@@@@@@@@@@                            13       
               8 |@@@@@@@@@@@@@@@@@@@@@                    21       
              16 |@@@@@                                    5        
              32 |                                         0        

  xterm                                             
           value  ------------- Distribution ------------- count    
              16 |                                         0        
              32 |@@@@@@@@@@@@@@@@@@@@@@@@                 19       
              64 |@@@@@@@@@                                7        
             128 |@@@@@@                                   5        
             256 |                                         0        

  fvwm2                                             
           value  ------------- Distribution ------------- count    
              -1 |                                         0        
               0 |@@@@@@@@@                                186      
               1 |                                         0        
               2 |                                         0        
               4 |@@                                       51       
               8 |                                         17       
              16 |                                         0        
              32 |@@@@@@@@@@@@@@@@@@@@@@@@@@               503      
              64 |                                         9        
             128 |                                         0        

  Xsun                                              
           value  ------------- Distribution ------------- count    
              -1 |                                         0        
               0 |@@@@@@@@@@@                              269      
               1 |                                         0        
               2 |                                         0        
               4 |                                         2        
               8 |@                                        31       
              16 |@@@@@                                    128      
              32 |@@@@@@@                                  171      
              64 |@                                        33       
             128 |@@@                                      85       
             256 |@                                        24       
             512 |                                         8        
            1024 |                                         21       
            2048 |@                                        26       
            4096 |                                         21       
            8192 |@@@@                                     94       
           16384 |                                         0

The sysinfo provider sets arg2 to be a pointer to a cpu_t, a structure internal to the kernel implementation. Most sysinfo probes fire on the CPU on which the statistic is being incremented, but some probes do not. The exceptional probes include cpu_ticks_idle, cpu_ticks_kernel, cpu_ticks_user and cpu_ticks_wait, which always fire on the CPU executing the system clock. Use the cpu_id member of the cpu_t structure to determine the CPU of interest. The following D script runs for about ten seconds and gives a quick snapshot of relative CPU behavior on a statistic-by-statistic basis:

cpu_ticks_*
{
        @[probename] = lquantize(((cpu_t *)arg2)->cpu_id, 0, 1024, 1);
}

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

Running the above script results in output similar to the following example:

# dtrace -s ./tick.d
dtrace: script './tick.d' matched 5 probes
CPU     ID                    FUNCTION:NAME
 22  37588                       :tick-1sec 

  cpu_ticks_user                                    
           value  ------------- Distribution ------------- count    
              11 |                                         0        
              12 |@@@@@@@@                                 14       
              13 |@@@@                                     7        
              14 |@                                        3        
              15 |@                                        2        
              16 |@@                                       4        
              17 |@@@@@@                                   10       
              18 |                                         0        
              19 |@                                        2        
              20 |@@@                                      6        
              21 |@@@                                      5        
              22 |                                         1        
              23 |@@@@@@                                   10       
              24 |                                         0        

  cpu_ticks_wait                                    
           value  ------------- Distribution ------------- count    
              11 |                                         0        
              12 |@@@@@@@@@@@@@                            241      
              13 |@@@@@@@@@@@@@                            236      
              14 |                                         16       
              15 |@@@@@@@                                  132      
              16 |                                         11       
              17 |                                         10       
              18 |                                         7        
              19 |@                                        18       
              20 |                                         4        
              21 |                                         16       
              22 |                                         13       
              23 |                                         10       
              24 |                                         0        

  cpu_ticks_kernel                                  
           value  ------------- Distribution ------------- count    
              11 |                                         0        
              12 |@@@@@@@@                                 234      
              13 |@@@@@                                    159      
              14 |@@@                                      104      
              15 |@@@@                                     131      
              16 |@@                                       66       
              17 |@                                        40       
              18 |@                                        51       
              19 |@                                        36       
              20 |@@                                       56       
              21 |@                                        42       
              22 |@@@                                      96       
              23 |@@                                       57       
              24 |                                         0        

  cpu_ticks_idle                                    
           value  ------------- Distribution ------------- count    
              11 |                                         0        
              12 |@@                                       534      
              13 |@@                                       621      
              14 |@@@                                      900      
              15 |@@                                       758      
              16 |@@@                                      942      
              17 |@@@                                      963      
              18 |@@@                                      965      
              19 |@@@                                      967      
              20 |@@@                                      957      
              21 |@@@                                      960      
              22 |@@@                                      913      
              23 |@@@                                      946      
              24 |                                         0