perf top: Move lost events warning to helpline

We can't display the UI box saying that we are slow in the reader
thread.  That will make 'perf top' even slower and the user even more
angry ;-)

Move the UI box message from the reader thread to the UI thread and
change it to a helpline, so there's no need to 'press any key'.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/n/tip-x4k0iuw7tt6mywsaguq6jfwu@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-top.c

@@ -553,8 +553,6 @@ static void perf_top__sort_new_samples(void *arg)
 	struct perf_evsel *evsel = t->sym_evsel;
 	struct hists *hists;
 
-	perf_top__reset_sample_counters(t);
-
 	if (t->evlist->selected != NULL)
 		t->sym_evsel = t->evlist->selected;
 
@@ -571,6 +569,11 @@ static void perf_top__sort_new_samples(void *arg)
 
 	hists__collapse_resort(hists, NULL);
 	perf_evsel__output_resort(evsel, NULL);
+
+	if (t->lost)
+		pr_warning("Too slow to read ring buffer (change period (-c/-F) or limit CPUs (-C)\n");
+
+	perf_top__reset_sample_counters(t);
 }
 
 static void *display_thread_tui(void *arg)
@@ -908,10 +911,8 @@ static void perf_top__mmap_read(struct perf_top *top)
 {
 	bool overwrite = top->record_opts.overwrite;
 	struct perf_evlist *evlist = top->evlist;
-	unsigned long long start, end;
 	int i;
 
-	start = rdclock();
 	if (overwrite)
 		perf_evlist__toggle_bkw_mmap(evlist, BKW_MMAP_DATA_PENDING);
 
@@ -922,13 +923,6 @@ static void perf_top__mmap_read(struct perf_top *top)
 		perf_evlist__toggle_bkw_mmap(evlist, BKW_MMAP_EMPTY);
 		perf_evlist__toggle_bkw_mmap(evlist, BKW_MMAP_RUNNING);
 	}
-	end = rdclock();
-
-	if ((end - start) > (unsigned long long)top->delay_secs * NSEC_PER_SEC)
-		ui__warning("Too slow to read ring buffer.\n"
-			    "Please try increasing the period (-c) or\n"
-			    "decreasing the freq (-F) or\n"
-			    "limiting the number of CPUs (-C)\n");
 }
 
 /*