感覺就不太是 context sw
for ex:
```
[root@vz15 ~]# /usr/bin/time -v ./app
PI = 3.141926
Command being timed: "./app"
User time (seconds): 4.74
System time (seconds): 0.00
Percent of CPU this job got: 99%
Elapsed (wall clock) time (h:mm:ss or m:ss): 0:04.75
Voluntary context switches: 1
Involuntary context switches: 11
[root@vz15 ~]# /usr/bin/time -v ./app
PI = 3.141926
Command being timed: "./app"
User time (seconds): 4.70
System time (seconds): 0.00
Percent of CPU this job got: 99%
Elapsed (wall clock) time (h:mm:ss or m:ss): 0:04.72
Voluntary context switches: 1
Involuntary context switches: 2753