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Directly call syscall(SYS_getpid) instead of getpid() in syscall test

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According to http://man7.org/linux/man-pages/man2/getpid.2.html:

> From glibc version 2.3.4 up to and including version 2.24, the glibc
wrapper function for getpid() cached PIDs, with the goal of avoiding
additional system calls when a process calls getpid() repeatedly.

So it's not suitable to messure the system call performance through
getpid(). Directly call syscall(SYS_getpid) is more appropriate.

From glibc version 2.25, cached pid is removed to fix some bugs which
makes the testsuite wrongly report performance regression on system call.

Same issue is reported to unixbench upstream long time ago, but nobody
cares. https://github.com/kdlucas/byte-unixbench/pull/58

Signed-off-by: Yuanhong Peng <yummypeng@linux.alibaba.com>

github: closes #58
This commit is contained in:
Yuanhong Peng 2020-10-23 16:17:03 +08:00 committed by Glenn Strauss
parent 070030e09f
commit 3d069b2e9c
1 changed files with 3 additions and 2 deletions
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5
UnixBench/src/syscall.c
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@ -28,6 +28,7 @@ char SCCSid[] = "@(#) @(#)syscall.c:3.3 -- 5/15/91 19:30:21";
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/syscall.h>
#include "timeit.c"
unsigned long iter;
@ -65,7 +66,7 @@ char *argv[];
case 'm':
while (1) {
close(dup(0));
getpid();
syscall(SYS_getpid);
getuid();
umask(022);
iter++;
@ -79,7 +80,7 @@ char *argv[];
/* NOTREACHED */
case 'g':
while (1) {
getpid();
syscall(SYS_getpid);
iter++;
}
/* NOTREACHED */