http://chadaustin.me/2015/04/thinking-about-performance/

gistfile1.txt

"fundamental constants of human-computer interaction", which can be split into the human and computer halves.

Very roughly:

~16 ms – frame budget for interactive animation
100 ms – user action feels instantaneous
200 ms – typical human reaction time
500+ ms – perceptible delay
3+ seconds – perceived sluggishness
10+ seconds – attention span is broken
And on the computer:

1 cycle – latency of simple bitwise operations
a few – maximum number of independent instructions that can be retired per cycle
3-4 cycles – latency of L1 cache hit
~dozen cycles – latency of L2 cache hit
~couple dozen cycles – integer division on modern x86
couple hundred cycles – round-trip to main memory
50-250 us – round-trip to SSD
250-1000 us – in-network ethernet/tcp round-trip
10 ms – spinny disk seek
150 ms – IP latency between Australia and USA
Throughput numbers:

8.5 GB/s – memory bandwidth on iPhone 5
~100 MB/s – saturated gigabit ethernet connection
50-100 MB/s – spinny disk transfer speed
4.5 Mb/s – global average connection speed
3.2 Mb/s – average mobile bandwidth in USA