tools/kvm_stat: reduce perceived idle time on filter updates

Whenever a user adds a filter, we
* redraw the header immediately for a snappy response
* print a message indicating to the user that we're busy while the
  noticeable delay induced by updating all of the stats objects takes place
* update the statistics ASAP (i.e. after 0.25s instead of 3s) to be
  consistent with behavior on startup
To do so, we split the Tui's refresh() method to allow for drawing header
and stats separately, and trigger a header refresh whenever we are about
to do something that takes a while - like updating filters.
Signed-off-by: NStefan Raspl <raspl@linux.vnet.ibm.com>
Signed-off-by: NRadim Krčmář <rkrcmar@redhat.com>

tools/kvm/kvm_stat/kvm_stat

@@ -801,6 +801,8 @@ class Stats(object):
 
 LABEL_WIDTH = 40
 NUMBER_WIDTH = 10
+DELAY_INITIAL = 0.25
+DELAY_REGULAR = 3.0
 
 
 class Tui(object):
@@ -856,13 +858,14 @@ class Tui(object):
         """Propagates pid selection to stats object."""
         self.stats.pid_filter = pid
 
-    def refresh(self, sleeptime):
-        """Refreshes on-screen data."""
+    def refresh_header(self, pid=None):
+        """Refreshes the header."""
+        if pid is None:
+            pid = self.stats.pid_filter
         self.screen.erase()
-        if self.stats.pid_filter > 0:
+        if pid > 0:
             self.screen.addstr(0, 0, 'kvm statistics - pid {0}'
-                               .format(self.stats.pid_filter),
-                               curses.A_BOLD)
+                               .format(pid), curses.A_BOLD)
         else:
             self.screen.addstr(0, 0, 'kvm statistics - summary', curses.A_BOLD)
         self.screen.addstr(2, 1, 'Event')
@@ -870,7 +873,13 @@ class Tui(object):
                            len('Total'), 'Total')
         self.screen.addstr(2, 1 + LABEL_WIDTH + NUMBER_WIDTH + 8 -
                            len('Current'), 'Current')
+        self.screen.addstr(4, 1, 'Collecting data...')
+        self.screen.refresh()
+
+    def refresh_body(self, sleeptime):
         row = 3
+        self.screen.move(row, 0)
+        self.screen.clrtobot()
         stats = self.stats.get()
 
         def sortkey(x):
@@ -914,10 +923,12 @@ class Tui(object):
             regex = self.screen.getstr()
             curses.noecho()
             if len(regex) == 0:
+                self.refresh_header()
                 return
             try:
                 re.compile(regex)
                 self.stats.fields_filter = regex
+                self.refresh_header()
                 return
             except re.error:
                 continue
@@ -944,37 +955,38 @@ class Tui(object):
 
             try:
                 pid = int(pid)
-
-                if pid == 0:
-                    self.update_pid(pid)
-                    break
-                else:
-                    if not os.path.isdir(os.path.join('/proc/', str(pid))):
-                        continue
-                    else:
-                        self.update_pid(pid)
-                        break
+                if pid != 0 and not os.path.isdir(os.path.join('/proc/',
+                                                               str(pid))):
+                    continue
+                self.refresh_header(pid)
+                self.update_pid(pid)
+                break
 
             except ValueError:
                 continue
 
     def show_stats(self):
         """Refreshes the screen and processes user input."""
-        sleeptime = 0.25
+        sleeptime = DELAY_INITIAL
+        self.refresh_header()
         while True:
-            self.refresh(sleeptime)
+            self.refresh_body(sleeptime)
             curses.halfdelay(int(sleeptime * 10))
-            sleeptime = 3.0
+            sleeptime = DELAY_REGULAR
             try:
                 char = self.screen.getkey()
                 if char == 'x':
+                    self.refresh_header()
                     self.update_drilldown()
+                    sleeptime = DELAY_INITIAL
                 if char == 'q':
                     break
                 if char == 'f':
                     self.show_filter_selection()
+                    sleeptime = DELAY_INITIAL
                 if char == 'p':
                     self.show_vm_selection()
+                    sleeptime = DELAY_INITIAL
             except KeyboardInterrupt:
                 break
             except curses.error: