Re: [Linux-fbdev-devel] [PATCH 1/2] vgacon: optimize scrolling

On Tue, Sep 23, 2008 at 11:59:18PM +0200, Krzysztof Helt wrote:

On Sun, 21 Sep 2008 23:22:17 +0200
Marcin Slusarz [off-list ref] wrote:

quoted

On Sun, Sep 21, 2008 at 08:37:57PM +0200, Krzysztof Helt wrote:

quoted

On Sun, 21 Sep 2008 18:00:08 +0200
Marcin Slusarz [off-list ref] wrote:

quoted

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
 

quoted

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).

This is not what I asked for. If the vgacon_scrollback_cnt is smaller then c->vc_rows it can happen.
The answer to my question is that count is always < vgacon_scrollback_cnt (set earlier before 
checking if it is in the <0,c->vc_rows> range).

Yep

(...)

quoted

quoted

quoted

+	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);

This line I got confused by. If the count is always smaller then
the vgacon_scrollback_cnt before (thus the vgacon_scrollback_size 
inside the if clause) this line always evaluates to copysize = count here.

You are right. I dropped this "call".
Thanks for a review.

---
Subject: [PATCH 1/2] vgacon: optimize scrolling

Join multiple scr_memcpyw into 1-3 calls (usually 2).
(benchmarked average speedup: 1%)

Signed-off-by: Marcin Slusarz <redacted>
Cc: Krzysztof Helt <redacted>
Cc: Antonino Daplas <adaplas@gmail.com>
Cc: linux-fbdev-devel@lists.sourceforge.net
---
 drivers/video/console/vgacon.c |   27 +++++++++++++++------------
 1 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/drivers/video/console/vgacon.c b/drivers/video/console/vgacon.c
index bd1f57b..29d1209 100644
--- a/drivers/video/console/vgacon.c
+++ b/drivers/video/console/vgacon.c

@@ -292,23 +292,26 @@ 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) {
+			scr_memcpyw(d, vgacon_scrollback, count);
+			d += count;
+		}
 	}
 
 	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