Fixed the pacing logic in bootchart data collection.

Ideally bootchart collects system data every BOOTCHART_POLLING_MS ms.
However, the current bootchart pacing logic would collect data every
time the main loop in init.c is executed. This results in:

1. Multiple data samples being taken consecutively or prematurely. In
many cases, these data samples have the same timestamp (in jiffies).
The off-line data processing tool would complain about dividing by
zero "interval" and bail out.

2. Because of the ineffective pacing, bootchart data collection would
terminate prematurely. The total duration of data collection is usually
much shorter than what the user specifies.

The fix is to check whether BOOTCHART_POLLING_MS ms has elapsed
before taking a new data sample. For this purpose, /proc/uptime
is used to get the time values, consistent with the precision of
bootchart timestamps.

Change-Id: I106bf91dbda01059b719df6c73b8bd1cd54a64f0
Signed-off-by: Bo (Andover) Zhang <zhang@broadcom.com>

init/bootchart.c

@@ -119,6 +119,18 @@ file_buff_done( FileBuff  buff )
     }
 }
 
+static long long
+get_uptime_jiffies()
+{
+    char       buff[64];
+    long long  jiffies = 0;
+
+    if (proc_read("/proc/uptime", buff, sizeof(buff)) > 0)
+        jiffies = 100LL*strtod(buff,NULL);
+
+    return jiffies;
+}
+
 static void
 log_header(void)
 {
@@ -185,22 +197,11 @@ static void
 do_log_uptime(FileBuff  log)
 {
     char  buff[65];
-    int   fd, ret, len;
+    int   len;
 
-    fd = open("/proc/uptime",O_RDONLY);
-    if (fd >= 0) {
-        int  ret;
-        ret = unix_read(fd, buff, 64);
-        close(fd);
-        buff[64] = 0;
-        if (ret >= 0) {
-            long long  jiffies = 100LL*strtod(buff,NULL);
-            int        len;
-            snprintf(buff,sizeof(buff),"%lld\n",jiffies);
-            len = strlen(buff);
-            file_buff_write(log, buff, len);
-        }
-    }
+    snprintf(buff,sizeof(buff),"%lld\n",get_uptime_jiffies());
+    len = strlen(buff);
+    file_buff_write(log, buff, len);
 }
 
 static void
@@ -376,3 +377,9 @@ void  bootchart_finish( void )
     file_buff_done(log_procs);
     acct(NULL);
 }
+
+/* called to get time (in ms) used by bootchart */
+long long  bootchart_gettime( void )
+{
+    return 10LL*get_uptime_jiffies();
+}

init/bootchart.h

@@ -26,6 +26,7 @@
 extern int   bootchart_init(void);
 extern int   bootchart_step(void);
 extern void  bootchart_finish(void);
+extern long long  bootchart_gettime(void);
 
 # define BOOTCHART_POLLING_MS   200   /* polling period in ms */
 # define BOOTCHART_DEFAULT_TIME_SEC    (2*60)  /* default polling time in seconds */

init/init.c

@@ -65,6 +65,7 @@ static int property_triggers_enabled = 0;
 
 #if BOOTCHART
 static int   bootchart_count;
+static long long bootchart_time = 0;
 #endif
 
 static char console[32];
@@ -1147,11 +1148,29 @@ int main(int argc, char **argv)
 
 #if BOOTCHART
         if (bootchart_count > 0) {
-            if (timeout < 0 || timeout > BOOTCHART_POLLING_MS)
-                timeout = BOOTCHART_POLLING_MS;
-            if (bootchart_step() < 0 || --bootchart_count == 0) {
-                bootchart_finish();
-                bootchart_count = 0;
+            long long current_time;
+            int elapsed_time, remaining_time;
+
+            current_time = bootchart_gettime();
+            elapsed_time = current_time - bootchart_time;
+
+            if (elapsed_time >= BOOTCHART_POLLING_MS) {
+                /* count missed samples */
+                while (elapsed_time >= BOOTCHART_POLLING_MS) {
+                    elapsed_time -= BOOTCHART_POLLING_MS;
+                    bootchart_count--;
+                }
+                /* count may be negative, take a sample anyway */
+                bootchart_time = current_time;
+                if (bootchart_step() < 0 || bootchart_count <= 0) {
+                    bootchart_finish();
+                    bootchart_count = 0;
+                }
+            }
+            if (bootchart_count > 0) {
+                remaining_time = BOOTCHART_POLLING_MS - elapsed_time;
+                if (timeout < 0 || timeout > remaining_time)
+                    timeout = remaining_time;
             }
         }
 #endif