Profiling git's test suite, Linus noted [1] that a disproportionately large amount of time was spent reading /proc/meminfo. This is done by the glibc functions get_phys_pages and get_avphys_pages, but they only need the MemTotal and MemFree fields, respectively. That same information can be obtained with a single syscall, sysinfo, instead of six: open, fstat, mmap, read, close, munmap. While sysinfo also provides more than necessary, it does a lot less work than what the kernel needs to do to provide the entire /proc/meminfo. Both strace -T and in-app microbenchmarks shows that the sysinfo() approach is roughly an order of magnitude faster. sysinfo() is much older than what glibc currently requires, so I don't think there's any reason to keep the old parsing code. Moreover, this makes get_[av]phys_pages work even in the absence of /proc. Linus noted that something as simple as 'bash -c "echo"' would trigger the reading of /proc/meminfo, but gdb says that many more applications than just bash are affected: Starting program: /bin/bash "-c" "echo" Breakpoint 1, __get_phys_pages () at ../sysdeps/unix/sysv/linux/getsysstats.c:283 283 ../sysdeps/unix/sysv/linux/getsysstats.c: No such file or directory. (gdb) bt So it seems that any application that uses qsort on a moderately sized array will incur this cost (once), which is obviously proportionately more expensive for lots of short-lived processes (such as the git test suite). [1] http://thread.gmane.org/gmane.linux.kernel/2019285 Signed-off-by: Rasmus Villemoes <rv@rasmusvillemoes.dk> * sysdeps/unix/sysv/linux/getsysstats.c (__get_phys_pages): Use sysinfo system call instead of parsing /proc/meminfo. * sysdeps/unix/sysv/linux/getsysstats.c (__get_avphys_pages): Likewise.
__get_nprocs is called from malloc code, but calls fgets_unlocked, which is not an ISO C or POSIX function. This patch fixes it to call a new __fgets_unlocked name instead. Note: there are various other uses of fgets_unlocked in glibc's libraries, and I haven't yet investigated which others might also be problematic (called directly or indirectly from standard functions) and so need to change to use __fgets_unlocked. Tested for x86_64 (testsuite, and that disassembly of installed shared libraries is unchanged by the patch). [BZ #17582] * libio/iofgets.c [weak_alias && !_IO_MTSAFE_IO] (__fgets_unlocked): Add alias of _IO_fgets. Use libc_hidden_def. * libio/iofgets_u.c (fgets_unlocked): Rename to __fgets_unlocked and define as weak alias of __fgets_unlocked. Use libc_hidden_weak. (__fgets_unlocked): Use libc_hidden_def. * include/stdio.h (__fgets_unlocked): Declare. Use libc_hidden_proto. * sysdeps/unix/sysv/linux/getsysstats.c (phys_pages_info): Use __fgets_unlocked instead of fgets_unlocked. * sysdeps/unix/sysv/linux/alpha/getsysstats.c (GET_NPROCS_CONF_PARSER): Likewise. * sysdeps/unix/sysv/linux/sparc/getsysstats.c (GET_NPROCS_CONF_PARSER): Likewise.
This patch removes conditionals on __ASSUME_O_CLOEXEC, and on O_CLOEXEC being defined, in sysdeps/unix/sysv/linux/, now that O_CLOEXEC support can be unconditionally assumed. The patch is conservative in what it changes and further followup cleanups may be possible. It may be possible to remove dl-opendir.c, but the patch does not do so, just removing a redundant undefine and redefine of __ASSUME_O_CLOEXEC. Also, __ASSUME_O_CLOEXEC is defined unconditionally for Hurd as well as Linux. Thus, if we decide that O_CLOEXEC support is a required feature of any glibc port, we could remove __ASSUME_O_CLOEXEC and all conditionals on it throughout glibc, rather than just cleaning up sysdeps/unix/sysv/linux/. Tested x86_64 that the disassembly of installed shared libraries is unchanged by this patch. * sysdeps/unix/sysv/linux/dl-opendir.c (__ASSUME_O_CLOEXEC): Do not undefine and redefine. * sysdeps/unix/sysv/linux/getsysstats.c (__get_nprocs) [O_CLOEXEC]: Make code unconditional. (__get_nprocs) [!O_CLOEXEC]: Remove conditional code. * sysdeps/unix/sysv/linux/shm_open.c: Do not include <kernel-features.h>. [O_CLOEXEC && !__ASSUME_O_CLOEXEC] (have_o_cloexec): Remove conditional variable definition. (shm_open) [O_CLOEXEC]: Make code unconditional. (shm_open) [!O_CLOEXEC || !__ASSUME_O_CLOEXEC]: Remove conditional code.
Now that files using __ASSUME_* macros have been made by <https://sourceware.org/ml/libc-alpha/2014-06/msg00543.html> to include <kernel-features.h> directly, any include from a file not using __ASSUME_* macros can safely be removed (as there will no longer be some other file relying on indirect inclusion via a header from which the include is being removed). This patch removes such unnecessary kernel-features.h includes. Tested x86_64 that disassembly of installed shared libraries is unchanged by this patch, except for line numbers in calls to __assert_fail from libc.so and ld.so. 2014-06-23 Joseph Myers <joseph@codesourcery.com> * nptl/createthread.c: Don't include kernel-features.h. * nptl/pthread_cancel.c: Likewise. * nptl/pthread_condattr_setclock.c: Likewise. * nptl/sysdeps/unix/sysv/linux/pt-raise.c: Likewise. * nptl/sysdeps/unix/sysv/linux/pthread_getcpuclockid.c: Likewise. * nptl/sysdeps/unix/sysv/linux/pthread_kill.c: Likewise. * nptl/sysdeps/unix/sysv/linux/pthread_sigqueue.c: Likewise. * nptl/sysdeps/unix/sysv/linux/raise.c: Likewise. * nptl/sysdeps/unix/sysv/linux/s390/s390-32/pt-vfork.S: Likewise. * nptl/sysdeps/unix/sysv/linux/s390/s390-32/vfork.S: Likewise. * nptl/sysdeps/unix/sysv/linux/s390/s390-64/pt-vfork.S: Likewise. * nptl/sysdeps/unix/sysv/linux/s390/s390-64/vfork.S: Likewise. * nptl/sysdeps/unix/sysv/linux/timer_create.c: Likewise. * nptl/sysdeps/unix/sysv/linux/timer_delete.c: Likewise. * nptl/sysdeps/unix/sysv/linux/timer_getoverr.c: Likewise. * nptl/sysdeps/unix/sysv/linux/timer_gettime.c: Likewise. * nptl/sysdeps/unix/sysv/linux/timer_routines.c: Likewise. * nptl/sysdeps/unix/sysv/linux/timer_settime.c: Likewise. * nscd/gai.c: Likewise. * nss/nss_db/db-open.c: Likewise. * sysdeps/generic/ldsodefs.h: Likewise. * sysdeps/sh/nptl/tls.h: Likewise. * sysdeps/unix/sysv/linux/aarch64/sigaction.c: Likewise. * sysdeps/unix/sysv/linux/aarch64/sigcontextinfo.h: Likewise. * sysdeps/unix/sysv/linux/aarch64/vfork.S: Likewise. * sysdeps/unix/sysv/linux/adjtime.c: Likewise. * sysdeps/unix/sysv/linux/alpha/xstatconv.h: Likewise. * sysdeps/unix/sysv/linux/arm/sigaction.c: Likewise. * sysdeps/unix/sysv/linux/arm/sigcontextinfo.h: Likewise. * sysdeps/unix/sysv/linux/check_pf.c: Likewise. * sysdeps/unix/sysv/linux/clock_getcpuclockid.c: Likewise. * sysdeps/unix/sysv/linux/clock_getres.c: Likewise. * sysdeps/unix/sysv/linux/clock_gettime.c: Likewise. * sysdeps/unix/sysv/linux/clock_nanosleep.c: Likewise. * sysdeps/unix/sysv/linux/clock_settime.c: Likewise. * sysdeps/unix/sysv/linux/dl-execstack.c: Likewise. * sysdeps/unix/sysv/linux/dl-osinfo.h: Likewise. * sysdeps/unix/sysv/linux/dl-sysdep.c: Likewise. * sysdeps/unix/sysv/linux/generic/futimesat.c: Likewise. * sysdeps/unix/sysv/linux/generic/poll.c: Likewise. * sysdeps/unix/sysv/linux/generic/wordsize-32/fcntl.c: Likewise. * sysdeps/unix/sysv/linux/generic/wordsize-32/fxstatat.c: Likewise. * sysdeps/unix/sysv/linux/generic/wordsize-32/pread.c: Likewise. * sysdeps/unix/sysv/linux/generic/wordsize-32/pread64.c: Likewise. * sysdeps/unix/sysv/linux/generic/wordsize-32/preadv.c: Likewise. * sysdeps/unix/sysv/linux/generic/wordsize-32/preadv64.c: Likewise. * sysdeps/unix/sysv/linux/generic/wordsize-32/pwrite.c: Likewise. * sysdeps/unix/sysv/linux/generic/wordsize-32/pwrite64.c: Likewise. * sysdeps/unix/sysv/linux/generic/wordsize-32/pwritev.c: Likewise. * sysdeps/unix/sysv/linux/generic/wordsize-32/pwritev64.c: Likewise. * sysdeps/unix/sysv/linux/getcwd.c: Likewise. * sysdeps/unix/sysv/linux/getpagesize.c: Likewise. * sysdeps/unix/sysv/linux/getsysstats.c: Likewise. * sysdeps/unix/sysv/linux/i386/fxstat.c: Likewise. * sysdeps/unix/sysv/linux/i386/lxstat.c: Likewise. * sysdeps/unix/sysv/linux/i386/mmap.S: Likewise. * sysdeps/unix/sysv/linux/i386/mmap64.S: Likewise. * sysdeps/unix/sysv/linux/i386/sigaction.c: Likewise. * sysdeps/unix/sysv/linux/i386/vfork.S: Likewise. * sysdeps/unix/sysv/linux/i386/xstat.c: Likewise. * sysdeps/unix/sysv/linux/ia64/system.c: Likewise. * sysdeps/unix/sysv/linux/if_index.c: Likewise. * sysdeps/unix/sysv/linux/ifaddrs.c: Likewise. * sysdeps/unix/sysv/linux/ifreq.c: Likewise. * sysdeps/unix/sysv/linux/ldsodefs.h: Likewise. * sysdeps/unix/sysv/linux/lutimes.c: Likewise. * sysdeps/unix/sysv/linux/m68k/vfork.S: Likewise. * sysdeps/unix/sysv/linux/microblaze/nptl/vfork.S: Likewise. * sysdeps/unix/sysv/linux/mips/mips32/accept4.c: Likewise. * sysdeps/unix/sysv/linux/mips/mips32/recvmmsg.c: Likewise. * sysdeps/unix/sysv/linux/mips/mips32/sendmmsg.c: Likewise. * sysdeps/unix/sysv/linux/mips/pread.c: Likewise. * sysdeps/unix/sysv/linux/mips/pread64.c: Likewise. * sysdeps/unix/sysv/linux/mips/pwrite.c: Likewise. * sysdeps/unix/sysv/linux/mips/pwrite64.c: Likewise. * sysdeps/unix/sysv/linux/mips/sigaction.c: Likewise. * sysdeps/unix/sysv/linux/mmap64.c: Likewise. * sysdeps/unix/sysv/linux/netlinkaccess.h: Likewise. * sysdeps/unix/sysv/linux/powerpc/chown.c: Likewise. * sysdeps/unix/sysv/linux/powerpc/dl-sysdep.c: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc32/clone.S: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc32/fpu/fe_mask.c: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc32/fpu/fe_nomask.c: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc32/getcontext.S: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc32/pread.c: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc32/pread64.c: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc32/pwrite.c: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc32/pwrite64.c: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc32/setcontext.S: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc32/swapcontext.S: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc32/vfork.S: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc64/fpu/fe_mask.c: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc64/fpu/fe_nomask.c: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc64/getcontext.S: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc64/makecontext.S: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc64/pread.c: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc64/pread64.c: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc64/pwrite.c: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc64/pwrite64.c: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc64/setcontext.S: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc64/swapcontext.S: Likewise. * sysdeps/unix/sysv/linux/powerpc/powerpc64/vfork.S: Likewise. * sysdeps/unix/sysv/linux/pread.c: Likewise. * sysdeps/unix/sysv/linux/pread64.c: Likewise. * sysdeps/unix/sysv/linux/prof-freq.c: Likewise. * sysdeps/unix/sysv/linux/pwrite.c: Likewise. * sysdeps/unix/sysv/linux/pwrite64.c: Likewise. * sysdeps/unix/sysv/linux/s390/s390-32/mmap.S: Likewise. * sysdeps/unix/sysv/linux/s390/s390-32/mmap64.S: Likewise. * sysdeps/unix/sysv/linux/s390/system.c: Likewise. * sysdeps/unix/sysv/linux/sh/pread.c: Likewise. * sysdeps/unix/sysv/linux/sh/pread64.c: Likewise. * sysdeps/unix/sysv/linux/sh/pwrite.c: Likewise. * sysdeps/unix/sysv/linux/sh/pwrite64.c: Likewise. * sysdeps/unix/sysv/linux/sigaction.c: Likewise. * sysdeps/unix/sysv/linux/sigpending.c: Likewise. * sysdeps/unix/sysv/linux/sigprocmask.c: Likewise. * sysdeps/unix/sysv/linux/sigsuspend.c: Likewise. * sysdeps/unix/sysv/linux/sparc/sparc64/xstatconv.c: Likewise. * sysdeps/unix/sysv/linux/sparc/system.c: Likewise. * sysdeps/unix/sysv/linux/syslog.c: Likewise. * sysdeps/unix/sysv/linux/system.c: Likewise. * sysdeps/unix/sysv/linux/testrtsig.h: Likewise. * sysdeps/unix/sysv/linux/timespec_get.c: Likewise. * sysdeps/unix/sysv/linux/ttyname.c: Likewise. * sysdeps/unix/sysv/linux/ttyname_r.c: Likewise. * sysdeps/unix/sysv/linux/utimensat.c: Likewise. * sysdeps/unix/sysv/linux/x86_64/sigaction.c: Likewise. * sysdeps/unix/sysv/linux/xstatconv.h: Likewise.
The implementation of __get_nprocs uses a stactic variable to cache
the value of the current number of processors. The caching breaks when
'time (NULL) == 0':
$ cat nproc.c
#include <stdio.h>
#include <time.h>
#include <sys/time.h>
int main(int argc, char *argv[])
{
time_t t;
struct timeval tv = {0, 0};
printf("settimeofday({0, 0}, NULL) = %d\n", settimeofday(&tv, NULL));
t = time(NULL);
printf("Time: %d, CPUs: %d\n", (unsigned int)t, get_nprocs());
return 0;
}
$ gcc -O3 nproc.c
$ ./a.out
settimeofday({0, 0}, NULL) = -1
Time: 1401311578, CPUs: 4
$ sudo ./a.out
settimeofday({0, 0}, NULL) = 0
Time: 0, CPUs: 0
The problem is with the condition used to check whether a cached
value should be returned or not:
static int cached_result;
static time_t timestamp;
time_t now = time (NULL);
time_t prev = timestamp;
atomic_read_barrier ();
if (now == prev)
return cached_result;
This patch fixes the problem by ensuring that 'cached_result' has
been set at least once before returning it.