第三列似乎perf script很接近，但不完全是正常运行时间，该时间戳来自哪里？除了访问采样事件之外，还有其他方法可以访问该时间戳吗？
$ perf record cat /proc/uptime
1392597.79 16669901.66
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.002 MB perf.data (19 samples) ]
$ perf script
cat 902536 1392640.417831: 1 cycles:u: ffffffffac000b47 [unknown] ([unknown])
cat 902536 1392640.417849: 1 cycles:u: ffffffffac000b47 [unknown] ([unknown])
cat 902536 1392640.417863: 3 cycles:u: ffffffffac000b47 [unknown] ([unknown])
cat 902536 1392640.417876: 10 cycles:u: ffffffffac000b47 [unknown] ([unknown])
cat 902536 1392640.417889: 33 cycles:u: ffffffffac000b47 [unknown] ([unknown])
cat 902536 1392640.417902: 108 cycles:u: ffffffffac000b47 [unknown] ([unknown])
cat 902536 1392640.417915: 351 cycles:u: ffffffffac000b47 [unknown] ([unknown])
cat 902536 1392640.417929: 1136 cycles:u: ffffffffac000b47 [unknown] ([unknown])
cat 902536 1392640.417942: 3657 cycles:u: ffffffffac000b47 [unknown] ([unknown])
cat 902536 1392640.417958: 11701 cycles:u: ffffffffac000b47 [unknown] ([unknown])
cat 902536 1392640.417998: 34018 cycles:u: ffffffffac000b47 [unknown] ([unknown])
cat 902536 1392640.418060: 55936 cycles:u: ffffffffac000b47 [unknown] ([unknown])
cat 902536 1392640.418117: 77496 cycles:u: ffffffffac000b47 [unknown] ([unknown])
cat 902536 1392640.418195: 110190 cycles:u: ffffffffac000163 [unknown] ([unknown])
cat 902536 1392640.418296: 140857 cycles:u: ffffffffac000163 [unknown] ([unknown])
cat 902536 1392640.418422: 166643 cycles:u: ffffffffac000b47 [unknown] ([unknown])
cat 902536 1392640.418589: 187277 cycles:u: ffffffffac000163 [unknown] ([unknown])
cat 902536 1392640.418763: 198929 cycles:u: 7fdb1734b9a8 _dl_addr+0x108 (/usr/lib/libc-2.31.so)
cat 902536 1392640.418959: 209655 cycles:u: ffffffffac000163 [unknown] ([unknown])