Profiling of vdso_test_random

[Adhemerval Zanella Netto]

On 04/09/24 08:41, Christophe Leroy 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
>     22.49%  vdso_test_getra  [vdso]               [.] __arch_chacha20_blocks_nostack
>     10.80%  vdso_test_getra  vdso_test_getrandom  [.] test_vdso_getrandom
>      8.89%  vdso_test_getra  [vdso]               [.] __kernel_getrandom
>      0.01%  vdso_test_getra  [kernel.kallsyms]    [k] finish_task_switch.isra.0
> 

After tinkering with vDSO build parameters (I had to remove the '-Bsymbolic'
and 'objdump -S') to get perf show the symbols I see on aarch64 with a reduced
vdso_test_random:

$ perf record ./vdso_test_getrandom bench-single
$ perf report
[...]
# Samples: 305  of event 'cycles:P'
# Event count (approx.): 5583551
#
# Overhead  Command          Shared Object        Symbol
# ........  ...............  ...................  .........................................
#
    44.27%  vdso_test_getra  [vdso]               [.] __arch_chacha20_blocks_nostack
    21.16%  vdso_test_getra  [vdso]               [.] __kernel_getrandom
     6.19%  vdso_test_getra  [kernel.kallsyms]    [k] task_mm_cid_work
     3.14%  vdso_test_getra  [kernel.kallsyms]    [k] perf_iterate_ctx
     2.96%  vdso_test_getra  vdso_test_getrandom  [.] test_vdso_getrandom
     2.48%  vdso_test_getra  [kernel.kallsyms]    [k] __memcg_slab_free_hook
     2.28%  vdso_test_getra  [kernel.kallsyms]    [k] next_uptodate_folio
     2.05%  vdso_test_getra  [kernel.kallsyms]    [k] _raw_spin_unlock_irq

It is what I would expect, so I am not sure why might be different on powerpc.