Re: [PATCH] fbuffer: improve toggle cursor performance

[Thomas Huth <thuth@redhat.com>]

On Wed, 27 May 2015 02:11:13 +0200
Greg Kurz <gkurz@linux.vnet.ibm.com> wrote:

> SLOF currently calls hv-logical-load and hv-logical-store for every pixel
> when enabling or disabling the cursor. This is suboptimal when writing one
> char at a time to the console since terminal-write always toggles the cursor.
> And this is precisely what grub is doing when the user wants to edit a menu
> entry... the result is an incredibly slow and barely usable interface.
> 
> The inner loop in fb8-toggle-cursor handles a contiguous region: it can be
> converted to hv-logical-memop. The result is 32 times less hcalls per char
> and a serious improvement in grub usability.

Good idea for an optimization!

> Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> ---
>  slof/fs/fbuffer.fs |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/slof/fs/fbuffer.fs b/slof/fs/fbuffer.fs
> index 756f05a..46b59bf 100644
> --- a/slof/fs/fbuffer.fs
> +++ b/slof/fs/fbuffer.fs
> @@ -99,8 +99,8 @@ CREATE bitmap-buffer 400 4 * allot
>  : fb8-toggle-cursor ( -- )
>  	line# fb8-line2addr column# fb8-columns2bytes +
>  	char-height 0 ?DO
> -		char-width screen-depth * 0 ?DO dup dup rb@ -1 xor swap rb! 1+ LOOP
> -		screen-width screen-depth * + char-width screen-depth * -
> +		dup dup 0 char-width screen-depth * 1 hv-logical-memop drop
> +		screen-width screen-depth * +
>  	LOOP drop
>  ;

If you use hv-logical-memop in this file here, you definitely break
board-js2x, since this is bare metal and hv-logical-memop is not
defined there.

I think you should either move the new function to board-qemu and handle
it there like it is done for hcall-invert-screen already, or we could
think of introducing a helper function that is defined by each board
which does the xor operation on a memory region (that way we could
maybe also unify hcall-invert-screen and fb8-invert-screen again).

 Thomas