[PATCH] fbuffer: improve toggle cursor performance

[Nikunj A Dadhania]

Greg Kurz <gkurz at linux.vnet.ibm.com> writes:

> On Wed, 27 May 2015 10:41:06 +0530
> Nikunj A Dadhania <nikunj at linux.vnet.ibm.com> wrote:
>
>> Greg Kurz <gkurz at linux.vnet.ibm.com> writes:
>> 
>> > 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.
>> >
>> > Signed-off-by: Greg Kurz <gkurz at 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 * +
>> 
>> Why did you drop "char-width screen-depth * -" in the new code? This is
>> not me mentioned in the description.
>> 
>
> This is because the current inner loop increments the address. When the loop
> ends, we're pointing at the next char, that is char-width * screen-depth bytes
> too far.
>
> In the new code, the address is duped on the stack before calling hv-logical-memop,
> so we don't need to fix it when proceeding to next line.

Ah ok, i missed that 1+ in the loop.

> In my first attempt, I forgot to drop the subtraction and got an interesting
> visual result :)

Regards
Nikunj