On Mon, Mar 22, 2021 at 10:05:05AM -0400, Mikulas Patocka wrote:
> This patch replaces a loop with a "tzcnt" instruction.
Are you sure that's an optimisation? The loop would execute very few
times under normal circumstances (a maximum of three times on x86).
Some numbers would be nice.
> Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
>
> Index: linux-2.6/fs/buffer.c
> ===================================================================
> --- linux-2.6.orig/fs/buffer.c
> +++ linux-2.6/fs/buffer.c
Are ... are you still using CVS?!
> @@ -1020,11 +1020,7 @@ grow_buffers(struct block_device *bdev,
> pgoff_t index;
> int sizebits;
>
> - sizebits = -1;
> - do {
> - sizebits++;
> - } while ((size << sizebits) < PAGE_SIZE);
> -
> + sizebits = PAGE_SHIFT - __ffs(size);
> index = block >> sizebits;
>
> /*
>
