Understanding cpu% in fio

Understanding cpu% in fio

[puvi]

Hi All,

  Could you kindly help me understand the cpu% reported in FIO output.

  I'm using a dat file with the following global parameters.

[global]
buffered=1
bs=128k
iodepth=16
numjobs=1
group_reporting=1
size=2000m
rw=read
runtime=180
time_based

  and in the result I get something like this

  cpu          : usr=0.08%, sys=98.63%, ctx=46607, majf=0, minf=768

  and I monitor the system level utilization using vmstat and they
point to different values ( lesser values).

  Looking at the code I see that fio does cpu% as cpu_time( from
rusage) / total elapsed time. In the above case I have 128 jobfiles
running. Does fio add the cpu_time of all threads and then divide by
elapsed time ( ~180s) ? Kindly correct me if I'm wrong.

Thanks.

~Puvi