udevd on very large systems: again

[George Beshers <gbeshers@sgi.com>]

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After some testing the following patch seems safe for dealing with computers
with more than 500 processors.  It occurred to me that it might be 
easier and
just as useful to note when udev is running on a large computer (e.g., >= 8p
and >= 16Gb of memory) and simply not worry about throttling at that point.

The patch should apply cleanly against udev-110.

Comments welcome.

George


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diff -Naur udev-110.Orig/udevd.c udev-110.new/udevd.c
--- udev-110.Orig/udevd.c	2007-05-01 08:33:39.000000000 -0400
+++ udev-110.new/udevd.c	2007-05-01 12:49:38.000000000 -0400
@@ -347,31 +347,21 @@
 
 static int cpu_count(void)
 {
-	int f;
-	char buf[65536];
+	FILE* f;
+	char buf[1024];
 	int len;
 	const char *pos;
 	int count = 0;
 
-	f = open("/proc/stat", O_RDONLY);
-	if (f == -1)
+	f = fopen("/proc/stat", "r");
+	if (f == NULL)
 		return -1;
 
-	len = read(f, buf, sizeof(buf)-1);
-	close(f);
-	if (len <= 0)
-		return -1;
-	buf[len] = '\0';
-
-	pos = strstr(buf, "cpu");
-	if (pos == NULL)
-		return -1;
-
-	while (pos != NULL) {
-		if (strncmp(pos, "cpu", 3) == 0 &&isdigit(pos[3]))
+	while (fgets(buf, 1024, f) != NULL) {
+		if (strncmp(buf, "cpu", 3) == 0 && isdigit(buf[3]))
 			count++;
-		pos = strstr(&pos[3], "cpu");
 	}
+	fclose(f);
 
 	if (count == 0)
 		return -1;
@@ -380,30 +370,46 @@
 
 static int running_processes(void)
 {
-	int f;
-	char buf[32768];
+	FILE* f;
+	char buf[1024];
 	int len;
-	int running;
+	int running = -1;
 	const char *pos;
+	int retries = 3;
 
-	f = open("/proc/stat", O_RDONLY);
-	if (f == -1)
-		return -1;
-
-	len = read(f, buf, sizeof(buf)-1);
-	close(f);
-	if (len <= 0)
-		return -1;
-	buf[len] = '\0';
-
-	pos = strstr(buf, "procs_running ");
-	if (pos == NULL)
-		return -1;
+	/*
+	 * The retries is probably overkill but the text display is
+	 * changing rapidly.on large systems (>= 512p) and so, while
+	 * I have not actually recorded an instance where the retry
+         * was used I would rather not have it fail.
+	 * 
+	 * An alternative approach would be to note when we are on
+	 * a fairly large system (8cpus and 16Gbytes say) at which
+	 * point throttling is probably not really necessary.
+	 */
+	do {
+		f = fopen("/proc/stat", "r");
+		if (f == NULL)
+			return -1;
+
+		while (fgets(buf, 1024, f) != NULL) {
+			pos = strstr(buf, "procs_running ");
+			if (pos != NULL) {
+				int res;
+				res = sscanf(pos, "procs_running %u",
+					     &running);
+				if (res == 1) {
+					fclose(f);
+					return running;
+				}
+				break;
+			}
+		}
 
-	if (sscanf(pos, "procs_running %u", &running) != 1)
-		return -1;
+		fclose(f);
+	} while (retries-- > 0);
 
-	return running;
+	return -1;
 }
 
 /* return the number of process es in our session, count only until limit */

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