Re: [PATCH -next] MIPS: fix debugfs_simple_attr.cocci warnings

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Fri, Jan 25, 2019 at 02:42:17AM +0000, YueHaibing wrote:
> Use DEFINE_DEBUGFS_ATTRIBUTE rather than DEFINE_SIMPLE_ATTRIBUTE
> for debugfs files.
> 
> Semantic patch information:
> Rationale: DEFINE_SIMPLE_ATTRIBUTE + debugfs_create_file()
> imposes some significant overhead as compared to
> DEFINE_DEBUGFS_ATTRIBUTE + debugfs_create_file_unsafe().

What kind of overhead is this adding, and how are you measuring it?

> 
> Generated by: scripts/coccinelle/api/debugfs/debugfs_simple_attr.cocci
> 
> Signed-off-by: YueHaibing <yuehaibing@huawei.com>
> ---
>  arch/mips/kernel/spinlock_test.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/mips/kernel/spinlock_test.c b/arch/mips/kernel/spinlock_test.c
> index ab4e3e1..509de1e 100644
> --- a/arch/mips/kernel/spinlock_test.c
> +++ b/arch/mips/kernel/spinlock_test.c
> @@ -35,7 +35,7 @@ static int ss_get(void *data, u64 *val)
>  	return 0;
>  }
>  
> -DEFINE_SIMPLE_ATTRIBUTE(fops_ss, ss_get, NULL, "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_ss, ss_get, NULL, "%llu\n");
>  
>  
>  
> @@ -114,14 +114,14 @@ static int multi_get(void *data, u64 *val)
>  	return 0;
>  }
>  
> -DEFINE_SIMPLE_ATTRIBUTE(fops_multi, multi_get, NULL, "%llu\n");
> +DEFINE_DEBUGFS_ATTRIBUTE(fops_multi, multi_get, NULL, "%llu\n");
>  
>  static int __init spinlock_test(void)
>  {
> -	debugfs_create_file("spin_single", S_IRUGO, mips_debugfs_dir, NULL,
> -			    &fops_ss);
> -	debugfs_create_file("spin_multi", S_IRUGO, mips_debugfs_dir, NULL,
> -			    &fops_multi);
> +	debugfs_create_file_unsafe("spin_single", 0444, mips_debugfs_dir,
> +				   NULL, &fops_ss);
> +	debugfs_create_file_unsafe("spin_multi", 0444, mips_debugfs_dir,
> +				   NULL, &fops_multi);
>  	return 0;
>  }
>  device_initcall(spinlock_test);

This is just testing code, right?  Why is using the unsafe methods
needed?

thanks,

greg k-h