Allocate unique fd for each parallel to avoid unexpected syscall test…

… result

If all the parallels dup the same fd 0 and share the same file reference
count, then the f_count will meet with heavy lock contention. The syscall
cost of dup/close will occupy only a few in the test result. Allocating
one unique fd for each parallel will reduce lots of the unexpected
lock contention cost. And it will fully perform the syscall cost of
dup/close.

If the parallel number is 1, the testing result with this patch is the
same with the original one on ICX server, which is expected. If the
parallel number is large, the testing result will accurately show the
syscall cost of dup/close without the impact of data sharing.

Signed-off-by: Jiebin Sun <[email protected]>

UnixBench/src/syscall.c

@@ -29,6 +29,7 @@ char SCCSid[] = "@(#) @(#)syscall.c:3.3 -- 5/15/91 19:30:21";
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <sys/syscall.h>
+#include <unistd.h>
 #include "timeit.c"
 
 unsigned long iter;
@@ -39,12 +40,23 @@ void report()
 	exit(0);
 }
 
+int create_fd()
+{
+	int fd[2];
+
+	if (pipe(fd) != 0 || close(fd[1]) != 0)
+	    exit(1);
+
+	return fd[0];
+}
+
 int main(argc, argv)
 int	argc;
 char	*argv[];
 {
         char   *test;
 	int	duration;
+	int	fd;
 
 	if (argc < 2) {
 		fprintf(stderr,"Usage: %s duration [ test ]\n", argv[0]);
@@ -64,17 +76,19 @@ char	*argv[];
 
         switch (test[0]) {
         case 'm':
+	   fd = create_fd();
 	   while (1) {
-		close(dup(0));
+		close(dup(fd));
 		syscall(SYS_getpid);
 		getuid();
 		umask(022);
 		iter++;
 	   }
 	   /* NOTREACHED */
         case 'c':
+           fd = create_fd();
            while (1) {
-                close(dup(0));
+                close(dup(fd));
                 iter++;
            }
            /* NOTREACHED */