How accurate is strace? (SOLVED)

[cat_n_mouse]

Greetings,

Can anyone tell me if the time shown with "strace -T" for each system call
is at all representative of the actual time taken when the program executes that sys_call?

For example I write a program in C with a printf("hello"); then I do a strace
with the -T option, amongst other things it displays:

write(1,"hello") <0.000050>

does it mean that the program will take 0.000050 (or 50 microseconds) to execute the printf statement or is it just relevant to strace?

Thanks.

[amigo]

I suspect that it has relevance only to strace, but you should probably ask somewhere else where there are more experienced users, like linuxquestions.org programming forum.

[cat_n_mouse]

Thanks amigo, I will do so.

[cat_n_mouse]

Solved.

I took amigos advice and this little pup went to play with the big dogs
over at linuxquestions.org

The answer lies with the kernel configuration options (CONFIG_HZ, CONFIG_NO_HZ, CONFIG_HIGH_RES_TIMERS) and hardware clocks precision.

Also running under any debugger/tracer (strace included) will incur a speed penalty,
I just didn't expect such an overhead (80uS in 100mS)