Xen devel - Jul 2012 - [PATCH] xentop.c: Change curses painting behavior to avoid flicker

Currently, xentop calls clear() before drawing the screen and calling
refresh().  This causes the entire screen to be repainted from scratch
on each call to refresh().  It is inefficient and causes visible flicker
when using xentop.

This patch fixes this by calling erase() instead of clear() which overwrites
the current screen with blanks instead.  The screen is then drawn as usual
in the top() function and refresh() is called.  This method allows curses
to only repaint the characters that have changed since the last call
to refresh(), thus avoiding the flicker and sending fewer characters to
the terminal.

In the event the screen becomes corrupted, this patch accepts a CTRL-L
keystroke from the user which will call clear() and force a repaint of
the entire screen.

Signed-off-by: Jason McCarver <slam@parasite.cc>

diff -r 42f76d536b11 -r b1bf5533d565 tools/xenstat/xentop/xentop.c
--- a/tools/xenstat/xentop/xentop.c	Tue Jul 03 13:39:01 2012 +0100
+++ b/tools/xenstat/xentop/xentop.c	Wed Jul 04 13:53:25 2012 -0500
@@ -57,6 +57,7 @@
 #endif
 
 #define KEY_ESCAPE ''\x1B''
+#define KEY_REPAINT ''\x0C''
 
 #ifdef HOST_SunOS
 /* Old curses library on Solaris takes non-const strings. Also, ERR interferes
@@ -383,6 +384,9 @@ static int handle_key(int ch)
 		case ''d'': case ''D'':
 			set_prompt("Delay(sec)", set_delay);
 			break;
+		case KEY_REPAINT:
+			clear();
+			break;
 		case ''q'': case ''Q'': case KEY_ESCAPE:
 			return 0;
 		}
@@ -1201,7 +1205,7 @@ int main(int argc, char **argv)
 		do {
 			gettimeofday(&curtime, NULL);
 			if(ch != ERR || (curtime.tv_sec - oldtime.tv_sec) >= delay) {
-				clear();
+				erase();
 				top();
 				oldtime = curtime;
 				refresh();

Jason McCarver writes ("[PATCH] xentop.c: Change curses painting behavior
to avoid flicker"):
> Currently, xentop calls clear() before drawing the screen and calling
> refresh().  This causes the entire screen to be repainted from scratch
> on each call to refresh().  It is inefficient and causes visible flicker
> when using xentop.
> 
> This patch fixes this by calling erase() instead of clear() which
overwrites
> the current screen with blanks instead.  The screen is then drawn as usual
> in the top() function and refresh() is called.  This method allows curses
> to only repaint the characters that have changed since the last call
> to refresh(), thus avoiding the flicker and sending fewer characters to
> the terminal.
> 
> In the event the screen becomes corrupted, this patch accepts a CTRL-L
> keystroke from the user which will call clear() and force a repaint of
> the entire screen.
> 
> Signed-off-by: Jason McCarver <slam@parasite.cc>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

However, I think this needs to wait for Xen 4.3.  We are currently in
the freeze for the 4.2 release.

Ian.

On Tue, 17 Jul 2012 14:24:22 +0100
Ian Jackson <Ian.Jackson@eu.citrix.com> wrote:
> Jason McCarver writes ("[PATCH] xentop.c: Change curses painting
behavior to avoid flicker"):
> > Currently, xentop calls clear() before drawing the screen and calling
> > refresh().  This causes the entire screen to be repainted from scratch
> > on each call to refresh().  It is inefficient and causes visible
flicker
> > when using xentop.
> > 
> > This patch fixes this by calling erase() instead of clear() which
overwrites
> > the current screen with blanks instead.  The screen is then drawn as
usual
> > in the top() function and refresh() is called.  This method allows
curses
> > to only repaint the characters that have changed since the last call
> > to refresh(), thus avoiding the flicker and sending fewer characters
to
> > the terminal.
> > 
> > In the event the screen becomes corrupted, this patch accepts a CTRL-L
> > keystroke from the user which will call clear() and force a repaint of
> > the entire screen.
> > 
> > Signed-off-by: Jason McCarver <slam@parasite.cc>
> 
> Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
> 
> However, I think this needs to wait for Xen 4.3.  We are currently in
> the freeze for the 4.2 release.
> 
> Ian.
I apologize in advance for the newb questions.  Is there anything I need
to do to help this patch make it into 4.3?  Will I need to re-post it
to the list again at a later date, or is my first post of this
sufficient assuming the patch remains unchanged?

Jason

On Wed, 2012-07-18 at 00:39 +0100, slam wrote:
> On Tue, 17 Jul 2012 14:24:22 +0100
> Ian Jackson <Ian.Jackson@eu.citrix.com> wrote:
> 
> > Jason McCarver writes ("[PATCH] xentop.c: Change curses painting
behavior to avoid flicker"):
> > > Currently, xentop calls clear() before drawing the screen and
calling
> > > refresh().  This causes the entire screen to be repainted from
scratch
> > > on each call to refresh().  It is inefficient and causes visible
flicker
> > > when using xentop.
> > > 
> > > This patch fixes this by calling erase() instead of clear() which
overwrites
> > > the current screen with blanks instead.  The screen is then drawn
as usual
> > > in the top() function and refresh() is called.  This method
allows curses
> > > to only repaint the characters that have changed since the last
call
> > > to refresh(), thus avoiding the flicker and sending fewer
characters to
> > > the terminal.
> > > 
> > > In the event the screen becomes corrupted, this patch accepts a
CTRL-L
> > > keystroke from the user which will call clear() and force a
repaint of
> > > the entire screen.
> > > 
> > > Signed-off-by: Jason McCarver <slam@parasite.cc>
> > 
> > Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
> > 
> > However, I think this needs to wait for Xen 4.3.  We are currently in
> > the freeze for the 4.2 release.
> > 
> > Ian.
> 
> I apologize in advance for the newb questions.  Is there anything I need
> to do to help this patch make it into 4.3?  Will I need to re-post it
> to the list again at a later date, or is my first post of this
> sufficient assuming the patch remains unchanged?
I''d recommend reposting once 4.3 opens just to remind us.

Ian.

slam writes ("Re: [PATCH] xentop.c: Change curses painting behavior to
avoid flicker"):
> I apologize in advance for the newb questions.  Is there anything I need
> to do to help this patch make it into 4.3?  Will I need to re-post it
> to the list again at a later date, or is my first post of this
> sufficient assuming the patch remains unchanged?
No need to apologise.  In theory I''d hope we remember this but in
practice we don''t have any formal tracking.

So if you can, please do repost this after 4.2 is released.

Thanks,
Ian.

On Wed, 2012-07-18 at 11:46 +0100, Ian Jackson wrote:
> slam writes ("Re: [PATCH] xentop.c: Change curses painting behavior to
avoid flicker"):
> > I apologize in advance for the newb questions.  Is there anything I
need
> > to do to help this patch make it into 4.3?  Will I need to re-post it
> > to the list again at a later date, or is my first post of this
> > sufficient assuming the patch remains unchanged?
> 
> No need to apologise.  In theory I''d hope we remember this but in
> practice we don''t have any formal tracking.
> 
> So if you can, please do repost this after 4.2 is released.
I''ve applied this to unstable (aka 4.3-pre) now.

Ian.