Profiling of vdso_test_random

[Jason A. Donenfeld]

On Wed, Sep 4, 2024 at 1:41 PM Christophe Leroy
<christophe.leroy at csgroup.eu> wrote:
>
> Hi,
>
> I'm done a 'perf record' on vdso_test_random reduced to vdso test only,
> and I get the following function usage profile.
>
> Do you see the same type of percentage on your platforms ?
>
> I would have expected most of the time to be spent in
> __arch_chacha20_blocks_nostack() but that's in fact not the case.
>
> # Samples: 61K of event 'task-clock:ppp'
> # Event count (approx.): 15463500000
> #
> # Overhead  Command          Shared Object        Symbol
>
> # ........  ...............  ...................
> ....................................
> #
>      57.74%  vdso_test_getra  [vdso]               [.] __c_kernel_getrandom

Can you run `perf top` to see which instructions are hot? There are
some smp barriers in there which might be significant.