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SubjectRe: [Linux-fbdev-devel] [PATCH 1/2] vgacon: optimize scrolling
On Sun, Sep 21, 2008 at 08:37:57PM +0200, Krzysztof Helt wrote:
> On Sun, 21 Sep 2008 18:00:08 +0200
> Marcin Slusarz <marcin.slusarz@gmail.com> wrote:
>
> > Join multiple scr_memcpyw into 1-3 calls (usually 2).
> > (benchmarked average speedup: 1%)
> >
>
> The scr_memcpyw is an inline function so there is no real call here.

... or it's defined to memcpy

> However, have you tested the patch with scroll range > 2 * vgacon_scrollback_size?
>
> It seems that your patch only handles scrolling if it is not bigger than 2 * vgacon_scrollback_size.

No. count is always within range <0, c->vc_rows> (look how it's computed
just before this loop). Second copy is needed only when end of screen
crosses end/beginning of scrollback (it's a circular buffer).

> Regards,
> Krzysztof
>
> > Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
> > Cc: Antonino Daplas <adaplas@gmail.com>
> > Cc: linux-fbdev-devel@lists.sourceforge.net
> > ---
> > drivers/video/console/vgacon.c | 28 ++++++++++++++++------------
> > 1 files changed, 16 insertions(+), 12 deletions(-)
> >
> > diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
> > index bd1f57b..de4f66c 100644
> > --- a/drivers/video/console/vgacon.c
> > +++ b/drivers/video/console/vgacon.c
> > @@ -292,23 +292,27 @@ static int vgacon_scrolldelta(struct vc_data *c, int lines)
> > d = (void *) c->vc_origin;
> > s = (void *) c->vc_screenbuf;
> >
> > - while (count--) {
> > - scr_memcpyw(d, vgacon_scrollback + soff, c->vc_size_row);
> > - d += c->vc_size_row;
> > - soff += c->vc_size_row;
> > -
> > - if (soff >= vgacon_scrollback_size)
> > - soff = 0;
> > + if (count) {
> > + int copysize;
> > + count *= c->vc_size_row;
> > + /* how much memory to end of buffer left? */
> > + copysize = min(count, vgacon_scrollback_size - soff);
> > + scr_memcpyw(d, vgacon_scrollback + soff, copysize);
> > + d += copysize;
> > + count -= copysize;
> > +
> > + if (count) {
> > + copysize = min(count, vgacon_scrollback_size);
> > + scr_memcpyw(d, vgacon_scrollback, copysize);
> > + d += copysize;
> > + }
> > }
> >
> > if (diff == c->vc_rows) {
> > vgacon_cursor(c, CM_MOVE);
> > } else {
> > - while (diff--) {
> > - scr_memcpyw(d, s, c->vc_size_row);
> > - d += c->vc_size_row;
> > - s += c->vc_size_row;
> > - }
> > + if (diff)
> > + scr_memcpyw(d, s, diff * c->vc_size_row);
> > }
> >
> > return 1;
> > --
> > 1.5.6.4


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