[PATCH] perf/ui/tui: don't force a refresh during progress update

[Patrick Palka]

Each call to tui_progress__update() would forcibly refresh the entire
screen.  This is somewhat inefficient and causes noticable flickering
during the startup of perf-report, especially on large/slow terminals.

It looks like the force-refresh in tui_progress__update() serves no
purpose other than to clear the screen so that the progress bar of a
previous operation does not subsume with that of a subsequent operation.
But we can do just that in a much more efficient manner by clearing only
the region that a previous progress bar may have occupied before
repainting the new progress bar.  Then the force-refresh could be
removed with no change in visuals.

This patch disables the slow force-refresh in tui_progress__update() and
instead calls SLsmg_fill_region() on the entire area that the progress
bar may occupy before repainting it.  This change makes the startup of
perf-report much faster and appear much "smoother".

It turns out that this was a big bottleneck in the startup speed of
perf-report -- with this patch, perf-report starts up ~1.6x faster (0.8s
vs 0.5s) on my machines.  (These numbers were measured by running "time
perf report" on an 8MB perf.data and pressing 'q' immediately.)

Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Patrick Palka <patrick@xxxxxxxxxxxx>
---
 tools/perf/ui/tui/progress.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/perf/ui/tui/progress.c b/tools/perf/ui/tui/progress.c
index 6c2184d..641049a 100644
--- a/tools/perf/ui/tui/progress.c
+++ b/tools/perf/ui/tui/progress.c
@@ -17,13 +17,14 @@ static void tui_progress__update(u64 curr, u64 total, const char *title)
 	if (total == 0)
 		return;
 
-	ui__refresh_dimensions(true);
+	ui__refresh_dimensions(false);
 	pthread_mutex_lock(&ui__lock);
 	y = SLtt_Screen_Rows / 2 - 2;
 	SLsmg_set_color(0);
 	SLsmg_draw_box(y, 0, 3, SLtt_Screen_Cols);
 	SLsmg_gotorc(y++, 1);
 	SLsmg_write_string((char *)title);
+	SLsmg_fill_region(y, 1, 1, SLtt_Screen_Cols - 2, ' ');
 	SLsmg_set_color(HE_COLORSET_SELECTED);
 	bar = ((SLtt_Screen_Cols - 2) * curr) / total;
 	SLsmg_fill_region(y, 1, 1, bar, ' ');
-- 
1.8.4.rc3

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