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>

1 files changed, 23 insertions, 0 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;