Date: Wed, 26 Oct 2011 17:02:00 +0400 From: Alexandr Matveev <timon@timon.net.nz> To: hackers@freebsd.org Subject: sigprocmask and fork Message-ID: <4EA804C8.2030900@timon.net.nz>
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Hi,
We are using FreeBSD 8.2 on our servers for high load projects.
When I was preparing system for production I saw strange (as I think)
behavior,
that leads to increased load on servers.
If I made truss on httpd (apache22) process, I saw too much sigprocmask
syscalls:
24822: sigprocmask(SIG_BLOCK,0x0,0x0) = 0 (0x0)
24822: sigprocmask(SIG_BLOCK,0x0,0x0) = 0 (0x0)
24822: sigprocmask(SIG_BLOCK,0x0,0x0) = 0 (0x0)
24822: sigprocmask(SIG_BLOCK,0x0,0x0) = 0 (0x0)
24822: sigprocmask(SIG_BLOCK,0x0,0x0) = 0 (0x0)
... too many lines ...
and
24822:
sigprocmask(SIG_BLOCK,SIGHUP|SIGINT|SIGQUIT|SIGKILL|SIGPIPE|SIGALRM|SIGTERM|SIGURG|SIGSTOP|SIGTSTP|SIGCONT|SIGCHLD|SIGTTIN|SIGTTOU|SIGIO|SIGXCPU|SIGXFSZ|SIGVTALRM|SIGPROF|S
IGWINCH|SIGINFO|SIGUSR1|SIGUSR2,0x0) = 0 (0x0)
24822: sigprocmask(SIG_SETMASK,0x0,0x0) = 0 (0x0)
24822:
sigprocmask(SIG_BLOCK,SIGHUP|SIGINT|SIGQUIT|SIGKILL|SIGPIPE|SIGALRM|SIGTERM|SIGURG|SIGSTOP|SIGTSTP|SIGCONT|SIGCHLD|SIGTTIN|SIGTTOU|SIGIO|SIGXCPU|SIGXFSZ|SIGVTALRM|SIGPROF|S
IGWINCH|SIGINFO|SIGUSR1|SIGUSR2,0x0) = 0 (0x0)
24822: sigprocmask(SIG_SETMASK,0x0,0x0) = 0 (0x0)
24822:
sigprocmask(SIG_BLOCK,SIGHUP|SIGINT|SIGQUIT|SIGKILL|SIGPIPE|SIGALRM|SIGTERM|SIGURG|SIGSTOP|SIGTSTP|SIGCONT|SIGCHLD|SIGTTIN|SIGTTOU|SIGIO|SIGXCPU|SIGXFSZ|SIGVTALRM|SIGPROF|S
IGWINCH|SIGINFO|SIGUSR1|SIGUSR2,0x0) = 0 (0x0)
24822: sigprocmask(SIG_SETMASK,0x0,0x0) = 0 (0x0)
... too many lines ...
but apache, and modules loaded from it do not call this directly.
I was trying to use DTRACE for getting information about syscalls, and I
got same result.
I wrote a tiny sample
code:
$ cat sigproc_test.c
#include<unistd.h>
main()
{
fork();
}
I ran it on FreeBSD with different compilers:
$ cc sigproc_test.c -o sigproc_test
$ truss ./sigproc_test 2>&1 | grep sigprocmask | wc -l
8
$ g++ sigproc_test.c -o sigproc_test
$ truss ./sigproc_test 2>&1 | grep sigprocmask | wc -l
20
Is it normal to make so many sigprocmask syscalls for such simple program?
For example, there is no sigprocmask syscalls when I run it on Debian
Linux.
Another sample. Here we have sigprocmask syscalls on Linux too, but
FreeBSD makes this syscall significantly more often:
$ cat test.c
#include<unistd.h>
main()
{
int i;
sleep(2);
for (i = 0; i<3; i++) {
int pid = fork();
if (!pid) {
sleep(0.5);
return 0;
}
sleep(2);
}
}
FreeBSD 8.2:
# truss -f ./test
... SKIPPED ...
48666:
sigprocmask(SIG_BLOCK,SIGHUP|SIGINT|SIGQUIT|SIGKILL|SIGPIPE|SIGALRM|SIGTERM|SIGURG|SIGSTOP|SIGTSTP|SIGCONT|SIGCHLD|SIGTTIN|SIGTTOU|SIGIO|SIGXCPU|SIGXFSZ|SIGVTALRM|SIGPROF|SIGWINCH|SIGINFO|SIGUSR1|SIGUSR2,0x0)
= 0 (0x0)
48666: sigprocmask(SIG_SETMASK,0x0,0x0) = 0 (0x0)
48666: __sysctl(0xbfbfe6a4,0x2,0x28192700,0xbfbfe6ac,0x0,0x0) = 0 (0x0)
48666:
sigprocmask(SIG_BLOCK,SIGHUP|SIGINT|SIGQUIT|SIGKILL|SIGPIPE|SIGALRM|SIGTERM|SIGURG|SIGSTOP|SIGTSTP|SIGCONT|SIGCHLD|SIGTTIN|SIGTTOU|SIGIO|SIGXCPU|SIGXFSZ|SIGVTALRM|SIGPROF|SIGWINCH|SIGINFO|SIGUSR1|SIGUSR2,0x0)
= 0 (0x0)
48666: sigprocmask(SIG_SETMASK,0x0,0x0) = 0 (0x0)
48666: nanosleep({2.000000000 }) = 0 (0x0)
48666: fork() = 48667 (0xbe1b)
48667: sigprocmask(SIG_SETMASK,0x0,0x0) = 0 (0x0)
48667:
sigprocmask(SIG_BLOCK,SIGHUP|SIGINT|SIGQUIT|SIGKILL|SIGPIPE|SIGALRM|SIGTERM|SIGURG|SIGSTOP|SIGTSTP|SIGCONT|SIGCHLD|SIGTTIN|SIGTTOU|SIGIO|SIGXCPU|SIGXFSZ|SIGVTALRM|SIGPROF|SIGWINCH|SIGINFO|SIGUSR1|SIGUSR2,0x0)
= 0 (0x0)
48667: sigprocmask(SIG_SETMASK,0x0,0x0) = 0 (0x0)
48667: process exit, rval = 0
48666: nanosleep({2.000000000 }) = 0 (0x0)
48666: fork() = 48669 (0xbe1d)
48669:
sigprocmask(SIG_BLOCK,SIGHUP|SIGINT|SIGQUIT|SIGKILL|SIGPIPE|SIGALRM|SIGTERM|SIGURG|SIGSTOP|SIGTSTP|SIGCONT|SIGCHLD|SIGTTIN|SIGTTOU|SIGIO|SIGXCPU|SIGXFSZ|SIGVTALRM|SIGPROF|SIGWINCH|SIGINFO|SIGUSR1|SIGUSR2,0x0)
= 0 (0x0)
48669: sigprocmask(SIG_SETMASK,0x0,0x0) = 0 (0x0)
48669: process exit, rval = 0
48666: nanosleep({2.000000000 }) = 0 (0x0)
48666: fork() = 48674 (0xbe22)
48674: sigprocmask(SIG_SETMASK,0x0,0x0) = 0 (0x0)
48674:
sigprocmask(SIG_BLOCK,SIGHUP|SIGINT|SIGQUIT|SIGKILL|SIGPIPE|SIGALRM|SIGTERM|SIGURG|SIGSTOP|SIGTSTP|SIGCONT|SIGCHLD|SIGTTIN|SIGTTOU|SIGIO|SIGXCPU|SIGXFSZ|SIGVTALRM|SIGPROF|SIGWINCH|SIGINFO|SIGUSR1|SIGUSR2,0x0)
= 0 (0x0)
48674: sigprocmask(SIG_SETMASK,0x0,0x0) = 0 (0x0)
48674: process exit, rval = 0
48666: nanosleep({2.000000000 }) = 0 (0x0)
48666:
sigprocmask(SIG_BLOCK,SIGHUP|SIGINT|SIGQUIT|SIGKILL|SIGPIPE|SIGALRM|SIGTERM|SIGURG|SIGSTOP|SIGTSTP|SIGCONT|SIGCHLD|SIGTTIN|SIGTTOU|SIGIO|SIGXCPU|SIGXFSZ|SIGVTALRM|SIGPROF|SIGWINCH|SIGINFO|SIGUSR1|SIGUSR2,0x0)
= 0 (0x0)
48666: sigprocmask(SIG_SETMASK,0x0,0x0) = 0 (0x0)
48666:
sigprocmask(SIG_BLOCK,SIGHUP|SIGINT|SIGQUIT|SIGKILL|SIGPIPE|SIGALRM|SIGTERM|SIGURG|SIGSTOP|SIGTSTP|SIGCONT|SIGCHLD|SIGTTIN|SIGTTOU|SIGIO|SIGXCPU|SIGXFSZ|SIGVTALRM|SIGPROF|SIGWINCH|SIGINFO|SIGUSR1|SIGUSR2,0x0)
= 0 (0x0)
48666: sigprocmask(SIG_SETMASK,0x0,0x0) = 0 (0x0)
48666: process exit, rval = 0
Linux:
# strace ./test
... SKIPPED ...
rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
rt_sigaction(SIGCHLD, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
nanosleep({2, 0}, 0x7fff0e6b7050) = 0
clone(child_stack=0,
flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD,
child_tidptr=0x7fb553b0d9d0) = 24310
rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
rt_sigaction(SIGCHLD, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
--- SIGCHLD (Child exited) @ 0 (0) ---
nanosleep({2, 0}, 0x7fff0e6b7050) = 0
clone(child_stack=0,
flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD,
child_tidptr=0x7fb553b0d9d0) = 24311
rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
rt_sigaction(SIGCHLD, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
--- SIGCHLD (Child exited) @ 0 (0) ---
nanosleep({2, 0}, 0x7fff0e6b7050) = 0
clone(child_stack=0,
flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD,
child_tidptr=0x7fb553b0d9d0) = 24312
rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0
rt_sigaction(SIGCHLD, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
--- SIGCHLD (Child exited) @ 0 (0) ---
nanosleep({2, 0}, 0x7fff0e6b7050) = 0
exit_group(0) = ?
--
Alexander Matveev
.masterhost
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