Add new tool for observing metaslab allocations

[prakashsurya]

No description provided.

[prakashsurya]

git-ab-pre-push is here: v1, v2

Note, this is dependent on https://github.com/delphix/zfs/pull/126 and https://github.com/delphix/zfs/pull/127.

[prakashsurya]

$ sudo estat metaslab-alloc -mlza rpool 10
01/30/20 - 22:13:29 UTC

 Tracing enabled... Hit Ctrl-C to end.
   microseconds                                       /dev/sda1, success
value range                 count ------------- Distribution ------------- 
[0, 10)                       205 |@@@@@@@@@@@@@@@@@@@@@@@@                
[10, 20)                      115 |@@@@@@@@@@@@@                           
[20, 30)                       27 |@@@                                     
[30, 40)                        3 |@                                       
[80, 90)                        1 |@                                       

   bytes                                              /dev/sda1, success
value range                 count ------------- Distribution ------------- 
[512, 1K)                      52 |@@@@@@                                  
[1K, 2K)                       40 |@@@@@                                   
[2K, 4K)                       57 |@@@@@@@                                 
[4K, 8K)                       97 |@@@@@@@@@@@                             
[8K, 16K)                      33 |@@@@                                    
[16K, 32K)                      2 |@                                       
[32K, 64K)                     70 |@@@@@@@@                                

                                       iops(/s)  avg latency(us)       stddev(us)  throughput(k/s)
/dev/sda1, success                           35               12               41             3613


                                       iops(/s)  throughput(k/s)
total                                        35             3613


01/30/20 - 22:13:40 UTC

^C