Number of io requests for each io_submit

Async io use io_submit calls. aio=native is used for async io. To get number of io requests for each io_submit from KVM VM,
here you go. My seq write 4k run on SSD. While capturing IOPS, make sure to trace io_submit perf events using below. 
sys_enter_io_submit, sys_exit_io_submit are mandatory. Essentially each io_submit call followed by *_io_getevents
which are irrelevant to present topic. 

 -e syscalls:sys_enter_io_submit -e syscalls:sys_exit_io_submit -e syscalls:sys_enter_io_getevents -e syscalls:sys_exit_io_getevents

Get Iops for this run.

write-4KiBIOPS 76971.9

Get Number of io_submits from captured perf.data. Number of enter_io_submits are fine. Ofcourse same number of exits will be there

[root@perf io-submit-write-4k]# perf script | grep io_submit | grep enter | wc -l
493370
[root@perf io-submit-write-4k]#
Get timestamp of io_submit events. (first and last)
First: 
qemu-kvm  3693 [025]  1914.589390: syscalls:sys_enter_io_submit: ctx_id: 0x7f3f18a61000, nr: 0x000000d1, iocbpp:
                     697 io_submit (/usr/lib64/libaio.so.1.0.1)
                       8 [unknown] ([unknown])
                       0 [unknown] ([unknown])

Last: 

qemu-kvm  3693 [001]  1949.737723: syscalls:sys_enter_io_submit: ctx_id: 0x7f3f18a61000, nr: 0x000000d1, iocbpp: 0x7ffd4e50b7b0
                 697 io_submit (/usr/lib64/libaio.so.1.0.1)
        7f3f1c6c9250 [unknown] ([unknown])
                   0 [unknown] ([unknown])

Number of submits per sec.
Time stamp diff: 1949.737723- 1914.589390 = 35.15
Number of submits:  493370

Submits/sec = 493370/35.15 = 14036.13086771
 IOPS metric is requests/second. We got submits per second. 
Number of requests per submit
requets/submission = (requests/sec) / (submits/sec)
                   =  76971.9 / 14036.130
                   =  5.483840631

So for my 4k write run number of requests per each submit are 5.48

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