Re: [PATCH] tools/testing/selftests/powerpc: Add Anton's null_syscall benchmark to the selftests

[Christophe Leroy]

Le 27/09/2016 Ã 16:10, Rui Teng a ÃcritÂ:
> From: Anton Blanchard <anton@xxxxxxxxxx>
>
> Pull in a version of Anton's null_syscall benchmark:
> http://ozlabs.org/~anton/junkcode/null_syscall.c
> Into tools/testing/selftests/powerpc/benchmarks.
>
> Suggested-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Signed-off-by: Anton Blanchard <anton@xxxxxxxxxx>
> Signed-off-by: Rui Teng <rui.teng@xxxxxxxxxxxxxxxxxx>
> ---
>   .../testing/selftests/powerpc/benchmarks/Makefile  |   2 +-
>   .../selftests/powerpc/benchmarks/null_syscall.c    | 157 +++++++++++++++++++++
>   2 files changed, 158 insertions(+), 1 deletion(-)
>   create mode 100644 tools/testing/selftests/powerpc/benchmarks/null_syscall.c

[...]

> +
> +static void do_null_syscall(unsigned long nr)
> +{
> +	unsigned long i;
> +
> +	for (i = 0; i < nr; i++)
> +		getppid();
> +}
> +

Looks like getppid() performs a rcu_read_lock(). Is that what we want ?

Shouldn't we use getpid() instead for a lighter syscall ?

Christophe