From e7447c22b4d8172b56e11bd81e49099dfab3b24b Mon Sep 17 00:00:00 2001
From: Peter Schiffer <pschiffe@redhat.com>
Date: Thu, 27 Aug 2015 17:52:53 +0200
Subject: [PATCH] Pidstat outputs values > 100% for %CPU

On systems with many short living processes pidstat could run out of
pre-allocated space for PIDs. This patch increases NR_PID_PREALLOC constant so
more space for PIDs is pre-allocated, but also adds possibility to re-allocate
this space if needed.
---
 pidstat.c | 71 ++++++++++++++++++++++++++++++++++---------------------
 pidstat.h |  2 +-
 2 files changed, 45 insertions(+), 28 deletions(-)

diff --git a/pidstat.c b/pidstat.c
index d24ae02..a8bf571 100644
--- a/pidstat.c
+++ b/pidstat.c
@@ -157,17 +157,37 @@ void salloc_pid_array(unsigned int len)
  */
 void salloc_pid(unsigned int len)
 {
-	int i;
+	short i;
 
 	for (i = 0; i < 3; i++) {
-		if ((st_pid_list[i] = (struct pid_stats *) malloc(PID_STATS_SIZE * len)) == NULL) {
-			perror("malloc");
+		if ((st_pid_list[i] = (struct pid_stats *) calloc(len, PID_STATS_SIZE)) == NULL) {
+			perror("calloc");
 			exit(4);
 		}
-		memset(st_pid_list[i], 0, PID_STATS_SIZE * len);
 	}
 }
 
+/*
+ ***************************************************************************
+ * Reallocate structures for PIDs to read.
+ ***************************************************************************
+ */
+void realloc_pid(void)
+{
+	short i;
+	unsigned int new_size = 2 * pid_nr;
+
+	for (i = 0; i < 3; i++) {
+		if ((st_pid_list[i] = (struct pid_stats *) realloc(st_pid_list[i], PID_STATS_SIZE * new_size)) == NULL) {
+			perror("realloc");
+			exit(4);
+		}
+		memset(st_pid_list[i] + pid_nr, 0, PID_STATS_SIZE * (new_size - pid_nr));
+	}
+
+	pid_nr = new_size;
+}
+
 /*
  ***************************************************************************
  * Free PID list structures.
@@ -917,36 +937,33 @@ void read_stats(int curr)
 			exit(4);
 		}
 
-		while (p < pid_nr) {
-
-			/* Get directory entries */
-			while ((drp = readdir(dir)) != NULL) {
-				if (isdigit(drp->d_name[0]))
-					break;
+		/* Get directory entries */
+		while ((drp = readdir(dir)) != NULL) {
+			if (!isdigit(drp->d_name[0])) {
+				continue;
 			}
-			if (drp) {
-				pst = st_pid_list[curr] + p++;
-				pid = atoi(drp->d_name);
 
-				if (read_pid_stats(pid, pst, &thr_nr, 0)) {
-					/* Process has terminated */
-					pst->pid = 0;
-				}
+			pst = st_pid_list[curr] + p++;
+			pid = atoi(drp->d_name);
 
-				else if (DISPLAY_TID(pidflag)) {
-					/* Read stats for threads in task subdirectory */
-					read_task_stats(curr, pid, &p);
-				}
+			if (read_pid_stats(pid, pst, &thr_nr, 0)) {
+				/* Process has terminated */
+				pst->pid = 0;
+			} else if (DISPLAY_TID(pidflag)) {
+				/* Read stats for threads in task subdirectory */
+				read_task_stats(curr, pid, &p);
 			}
-			else {
-				for (q = p; q < pid_nr; q++) {
-					pst = st_pid_list[curr] + q;
-					pst->pid = 0;
-				}
-				break;
+
+			if (p >= pid_nr) {
+				realloc_pid();
 			}
 		}
 
+		for (q = p; q < pid_nr; q++) {
+			pst = st_pid_list[curr] + q;
+			pst->pid = 0;
+		}
+
 		/* Close /proc directory */
 		closedir(dir);
 	}
diff --git a/pidstat.h b/pidstat.h
index 0a72468..2fd5980 100644
--- a/pidstat.h
+++ b/pidstat.h
@@ -13,7 +13,7 @@
 #define K_P_CHILD	"CHILD"
 #define K_P_ALL		"ALL"
 
-#define NR_PID_PREALLOC	10
+#define NR_PID_PREALLOC	100
 
 #define MAX_COMM_LEN	128
 #define MAX_CMDLINE_LEN	128
-- 
2.40.0