What is the difference between the events task-clock and cpu-clock?

[Andreas Hollmann <hollmann@in.tum.de>]

Hi,

what's the difference between the two events task-clock and cpu-clock?

I couldn't find any information that tells me the difference.

Why does the event modifier 'u' has no effect on these two software events?

Cheers,
Andreas

Here is the example:

$ time perf stat -e
'{task-clock,task-clock:u,cpu-clock,cpu-clock:u,instructions,instructions:u}'
dd if=/dev/zero of=/dev/null count=10000000
10000000+0 records in
10000000+0 records out
5120000000 bytes (5.1 GB) copied, 2.99018 s, 1.7 GB/s

 Performance counter stats for 'dd if=/dev/zero of=/dev/null count=10000000':

       2989.907827 task-clock                #    0.999 CPUs utilized
       2989.907827 task-clock:u              #    0.999 CPUs utilized
       2989.992015 cpu-clock
       2989.999305 cpu-clock:u
    14,525,479,811 instructions              #    0.00  insns per cycle
     3,130,315,989 instructions:u            #    0.00  insns per cycle

       2.991410383 seconds time elapsed


real    0m3.001s
user    0m0.723s
sys     0m2.270s