perf-simple-query: add mean and standard deviation stats
Currently, perf-simple-query summarizes the statistics
only for the throughput, printing the median,
median absolute deviation, minimum, and maximum.
But the throughput put is typically highly variable
and its median is noisy.
This patch calculates also the mean and standard deviation
and does that also for instructions_per_op and cpu_cycles_per_op
to present a fuller picture of the performance metrics.
Output example:
```
random-seed=3383668492
enable-cache=1
Running test with config: {partitions=10000, concurrency=100, mode=read, frontend=cql, query_single_key=no, counters=no}
Disabling auto compaction
Creating 10000 partitions...
95613.97 tps ( 63.1 allocs/op, 0.0 logallocs/op, 14.1 tasks/op, 42456 insns/op, 22117 cycles/op, 0 errors)
97538.45 tps ( 63.1 allocs/op, 0.0 logallocs/op, 14.1 tasks/op, 42454 insns/op, 22094 cycles/op, 0 errors)
95883.37 tps ( 63.1 allocs/op, 0.0 logallocs/op, 14.1 tasks/op, 42438 insns/op, 22268 cycles/op, 0 errors)
96791.45 tps ( 63.1 allocs/op, 0.0 logallocs/op, 14.1 tasks/op, 42433 insns/op, 22256 cycles/op, 0 errors)
97894.71 tps ( 63.1 allocs/op, 0.0 logallocs/op, 14.1 tasks/op, 42420 insns/op, 22010 cycles/op, 0 errors)
throughput: mean=96744.39 standard-deviation=996.89 median=96791.45 median-absolute-deviation=861.02 maximum=97894.71 minimum=95613.97
instructions_per_op: mean=42440.08 standard-deviation=14.99 median=42437.59 median-absolute-deviation=13.58 maximum=42456.15 minimum=42420.10
cpu_cycles_per_op: mean=22148.98 standard-deviation=110.43 median=22117.04 median-absolute-deviation=106.89 maximum=22267.70 minimum=22010.42
```
Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
Closes scylladb/scylladb#19450
3f23016cc0