perf hists browser: Recalculate browser pointers after resort/decay

In browsers that access dynamic underlying data structures, like in the
hists browser and its hist_entry rb_tree, we need to revalidate any
reference to the underlying data structure, because they can have gone
away, decayed.

This fixes a problem where after a while the top entries get behind the
top of the screen, i.e. the top_idx stays at 0, which means it is at the
first entry in the rb_tree when in fact it wasn't because the
browser->top didn't got revalidated after the timer ran and the
underlying data structure got updated.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-mhje66qssdko24q67a2lhlho@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

3 files changed, 26 insertions, 7 deletions

diff --git a/tools/perf/util/ui/browser.c b/tools/perf/util/ui/browser.c
index 611219f80680..5911bba63858 100644
--- a/tools/perf/util/ui/browser.c
+++ b/tools/perf/util/ui/browser.c
@@ -230,6 +230,29 @@ int ui_browser__refresh(struct ui_browser *self)
         return 0;
 }
 
+/*
+ * Here we're updating nr_entries _after_ we started browsing, i.e.  we have to
+ * forget about any reference to any entry in the underlying data structure,
+ * that is why we do a SEEK_SET. Think about 'perf top' in the hists browser
+ * after an output_resort and hist decay.
+ */
+void ui_browser__update_nr_entries(struct ui_browser *browser, u32 nr_entries)
+{
+        off_t offset = nr_entries - browser->nr_entries;
+
+        browser->nr_entries = nr_entries;
+
+        if (offset < 0) {
+                if (browser->top_idx < (u64)-offset)
+                        offset = -browser->top_idx;
+
+                browser->index += offset;
+                browser->top_idx += offset;
+        }
+
+        browser->seek(browser, browser->top_idx, SEEK_SET);
+}
+
 int ui_browser__run(struct ui_browser *self)
 {
         struct newtExitStruct es;
diff --git a/tools/perf/util/ui/browser.h b/tools/perf/util/ui/browser.h
index fc63dda10910..d42be43ac0e8 100644
--- a/tools/perf/util/ui/browser.h
+++ b/tools/perf/util/ui/browser.h
@@ -41,6 +41,7 @@ int ui_browser__show(struct ui_browser *self, const char *title,
 void ui_browser__hide(struct ui_browser *self);
 int ui_browser__refresh(struct ui_browser *self);
 int ui_browser__run(struct ui_browser *self);
+void ui_browser__update_nr_entries(struct ui_browser *browser, u32 nr_entries);
 
 void ui_browser__rb_tree_seek(struct ui_browser *self, off_t offset, int whence);
 unsigned int ui_browser__rb_tree_refresh(struct ui_browser *self);
diff --git a/tools/perf/util/ui/browsers/hists.c b/tools/perf/util/ui/browsers/hists.c
index e64d9527f14e..9ece84353538 100644
--- a/tools/perf/util/ui/browsers/hists.c
+++ b/tools/perf/util/ui/browsers/hists.c
@@ -332,13 +332,7 @@ static int hist_browser__run(struct hist_browser *self, const char *ev_name,
                 case -1:
                         /* FIXME we need to check if it was es.reason == NEWT_EXIT_TIMER */
                         timer(arg);
-                        /*
-                         * The timer may have changed the number of entries.
-                         * XXX: Find better way to keep this in synch, probably
-                         * removing this timer function altogether and just sync
-                         * using the hists->lock...
-                         */
-                        self->b.nr_entries = self->hists->nr_entries;
+                        ui_browser__update_nr_entries(&self->b, self->hists->nr_entries);
                         hists__browser_title(self->hists, title, sizeof(title),
                                              ev_name, self->dso_filter,
                                              self->thread_filter);
@@ -985,6 +979,7 @@ do_annotate:
 
                         hist_entry__tui_annotate(he, evsel->idx, nr_events,
                                                  timer, arg, delay_secs);
+                        ui_browser__update_nr_entries(&browser->b, browser->hists->nr_entries);
                 } else if (choice == browse_map)
                         map__browse(browser->selection->map);
                 else if (choice == zoom_dso) {