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I would like to ask question about the output from sar -q . I appreciate if someone can help me out with understanding runq-sz.

I have a system which cpu threads are 8 cpu threads on RHEL 7.2 .

[ywatanabe@host2 ~]$ cat /proc/cpuinfo | grep processor | wc -l
8

Below is sar -q result from my system but runq-sz seems to be low compared to ldavg-1 .

 runq-sz plist-sz ldavg-1 ldavg-5 ldavg-15 blocked
05:10:01 PM 0 361 0.29 1.68 2.14 0
05:11:01 PM 0 363 1.18 1.61 2.08 2
05:12:01 PM 0 363 7.03 3.15 2.58 1
05:13:01 PM 0 365 8.12 4.15 2.96 1
05:14:01 PM 3 371 7.40 4.64 3.20 1
05:15:01 PM 2 370 7.57 5.26 3.51 1
05:16:01 PM 0 366 8.42 5.90 3.84 1
05:17:01 PM 0 365 8.78 6.45 4.16 1
05:18:01 PM 0 363 7.05 6.40 4.28 2
05:19:02 PM 1 364 8.05 6.74 4.53 0
05:20:01 PM 0 367 7.96 6.96 4.74 1
05:21:01 PM 0 367 7.86 7.11 4.93 1
05:22:01 PM 1 366 7.84 7.31 5.14 0

From the man sar , I was thinking that runq-sz represents the number of tasks inside the run queue which states are TASK_RUNNING which corresponds to R sate in ps .

 runq-sz
 Run queue length (number of tasks waiting for run time).

What does runq-sz actually represent ?

This man page has a more detailed explanation of this property:

runq-sz

The number of kernel threads in memory that are waiting for a CPU to run. Typically, this value should be less than 2. Consistently higher values mean that the system might be CPU-bound.

Interpreting results

As is the case with many "indicators" you have to use them in combination with one another to interpret if there's a performance issue or not. This particular indicator indicates if your system is starved for CPU time.

Whereas the load1,5,15 indicate processes that are in the run queue, but are being forced to wait for time to run. The load1,5,15 variety tells you the general trend of the system and if it's got a lot of processes waiting (ramping up load) vs. trending down. But processes can wait for a variety of things with load1,5,15, typically it's I/O that's blocking when you see high load1,5,15 times.

With runq-sz, you're waiting for time on a CPU.

References

• How to Check Queue Activity (sar -q)