Re: [PATCH] btrfs: do not evaluate the expression with !CONFIG_BTRFS_ASSERT

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Fri, Jul 24, 2020 at 12:41:47PM -0400, Josef Bacik wrote:
> While investigating a performance issue I noticed that turning off
> CONFIG_BTRFS_ASSERT had no effect in what I was seeing in perf,
> specifically check_setget_bounds() was around 5% for this workload.
> Upon investigation I realized that I made a mistake when I added
> ASSERT(), I would still evaluate the expression, but simply ignore the
> result.
> 
> This is useless, and has a marked impact on performance.  This
> microbenchmark is the watered down version of an application that is
> experiencing performance issues, and does renames and creates over and
> over again.  Doing these operations 200k times without this patch takes
> 13 seconds on my machine.  With this patch it takes 7 seconds.
> 
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>

lolz,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> ---
>  fs/btrfs/ctree.h        | 2 +-
>  fs/btrfs/struct-funcs.c | 2 ++
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 9c7e466f27a9..b0fe8cca7e86 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -3238,7 +3238,7 @@ static inline void assertfail(const char *expr, const char *file, int line)
>  
>  #else
>  static inline void assertfail(const char *expr, const char* file, int line) { }
> -#define ASSERT(expr)	(void)(expr)
> +#define ASSERT(expr)	((void)0)
>  #endif
>  
>  /*
> diff --git a/fs/btrfs/struct-funcs.c b/fs/btrfs/struct-funcs.c
> index 079b059818e9..f44dc1207792 100644
> --- a/fs/btrfs/struct-funcs.c
> +++ b/fs/btrfs/struct-funcs.c
> @@ -17,6 +17,7 @@ static inline void put_unaligned_le8(u8 val, void *p)
>         *(u8 *)p = val;
>  }
>  
> +#ifdef CONFIG_BTRFS_ASSERT
>  static bool check_setget_bounds(const struct extent_buffer *eb,
>  				const void *ptr, unsigned off, int size)
>  {
> @@ -37,6 +38,7 @@ static bool check_setget_bounds(const struct extent_buffer *eb,
>  
>  	return true;
>  }
> +#endif
>  
>  /*
>   * Macro templates that define helpers to read/write extent buffer data of a
> -- 
> 2.24.1
>