How to understand percents in perf? - c++

Question

Consider the following application.
#include <cmath>
void foo()
{
double x = 42.0;
for ( unsigned long i = 0; i < 10000000; ++i )
x = std::sin( x );
}
int main()
{
foo();
return 0;
}
I use the following commands.
g++ main.cpp
perf record ./a.out
perf report
And I see.
Samples: 518 of event 'cycles', Event count (approx.): 410229343
Overhead Command Shared Object Symbol
84,28% a.out libm.so.6 [.] __subtf3
12,59% a.out a.out [.] foo
2,47% a.out a.out [.] _init
0,47% a.out [kernel.kallsyms] [k] may_open
0,17% a.out [kernel.kallsyms] [k] memcg_slab_post_alloc_hook
0,01% perf-ex [kernel.kallsyms] [k] mutex_unlock
0,01% a.out [kernel.kallsyms] [k] __intel_pmu_enable_all.constprop.0
0,00% perf-ex [kernel.kallsyms] [k] native_write_msr
0,00% a.out [kernel.kallsyms] [k] native_write_msr
How to understand 12,59% for foo?
How to tell perf report to show full percent of time spent in a function? I want to see something like - foo 99%, __subtf3 90%.

Answer 1

This is a half of an answer. I will answer myself on the second question.
Use the following command to see percents as you wish.
perf record -e cpu-cycles --call-graph dwarf,4096 -F 250 ./a.out
perf report
And the result will look like.
+ 100,00% 0,00% a.out a.out [.] _start
+ 100,00% 0,00% a.out libc.so.6 [.] __libc_start_main_impl (inlined)
+ 100,00% 0,00% a.out libc.so.6 [.] __libc_start_call_main (inlined)
+ 100,00% 0,00% a.out a.out [.] main
+ 100,00% 16,27% a.out a.out [.] foo
+ 83,73% 0,00% a.out libm.so.6 [.] __sin_fma (inlined)
+ 83,73% 83,73% a.out libm.so.6 [.] __subtf3
+ 62,87% 0,00% a.out libm.so.6 [.] do_sin (inlined)
+ 5,85% 0,00% a.out libm.so.6 [.] libc_feholdsetround_sse_ctx (inlined)
...