Go to file
Stefan Liebler 12d2dd7060 Optimize generic spinlock code and use C11 like atomic macros.
This patch optimizes the generic spinlock code.

The type pthread_spinlock_t is a typedef to volatile int on all archs.
Passing a volatile pointer to the atomic macros which are not mapped to the
C11 atomic builtins can lead to extra stores and loads to stack if such
a macro creates a temporary variable by using "__typeof (*(mem)) tmp;".
Thus, those macros which are used by spinlock code - atomic_exchange_acquire,
atomic_load_relaxed, atomic_compare_exchange_weak - have to be adjusted.
According to the comment from  Szabolcs Nagy, the type of a cast expression is
unqualified (see http://www.open-std.org/jtc1/sc22/wg14/www/docs/dr_423.htm):
__typeof ((__typeof (*(mem)) *(mem)) tmp;
Thus from spinlock perspective the variable tmp is of type int instead of
type volatile int.  This patch adjusts those macros in include/atomic.h.
With this construct GCC >= 5 omits the extra stores and loads.

The atomic macros are replaced by the C11 like atomic macros and thus
the code is aligned to it.  The pthread_spin_unlock implementation is now
using release memory order instead of sequentially consistent memory order.
The issue with passed volatile int pointers applies to the C11 like atomic
macros as well as the ones used before.

I've added a glibc_likely hint to the first atomic exchange in
pthread_spin_lock in order to return immediately to the caller if the lock is
free.  Without the hint, there is an additional jump if the lock is free.

I've added the atomic_spin_nop macro within the loop of plain reads.
The plain reads are also realized by C11 like atomic_load_relaxed macro.

The new define ATOMIC_EXCHANGE_USES_CAS determines if the first try to acquire
the spinlock in pthread_spin_lock or pthread_spin_trylock is an exchange
or a CAS.  This is defined in atomic-machine.h for all architectures.

The define SPIN_LOCK_READS_BETWEEN_CMPXCHG is now removed.
There is no technical reason for throwing in a CAS every now and then,
and so far we have no evidence that it can improve performance.
If that would be the case, we have to adjust other spin-waiting loops
elsewhere, too!  Using a CAS loop without plain reads is not a good idea
on many targets and wasn't used by one.  Thus there is now no option to
do so.

Architectures are now using the generic spinlock automatically if they
do not provide an own implementation.  Thus the pthread_spin_lock.c files
in sysdeps folder are deleted.

ChangeLog:

	* NEWS: Mention new spinlock implementation.
	* include/atomic.h:
	(__atomic_val_bysize): Cast type to omit volatile qualifier.
	(atomic_exchange_acq): Likewise.
	(atomic_load_relaxed): Likewise.
	(ATOMIC_EXCHANGE_USES_CAS): Check definition.
	* nptl/pthread_spin_init.c (pthread_spin_init):
	Use atomic_store_relaxed.
	* nptl/pthread_spin_lock.c (pthread_spin_lock):
	Use C11-like atomic macros.
	* nptl/pthread_spin_trylock.c (pthread_spin_trylock):
	Likewise.
	* nptl/pthread_spin_unlock.c (pthread_spin_unlock):
	Use atomic_store_release.
	* sysdeps/aarch64/nptl/pthread_spin_lock.c: Delete File.
	* sysdeps/arm/nptl/pthread_spin_lock.c: Likewise.
	* sysdeps/hppa/nptl/pthread_spin_lock.c: Likewise.
	* sysdeps/m68k/nptl/pthread_spin_lock.c: Likewise.
	* sysdeps/microblaze/nptl/pthread_spin_lock.c: Likewise.
	* sysdeps/mips/nptl/pthread_spin_lock.c: Likewise.
	* sysdeps/nios2/nptl/pthread_spin_lock.c: Likewise.
	* sysdeps/aarch64/atomic-machine.h (ATOMIC_EXCHANGE_USES_CAS): Define.
	* sysdeps/alpha/atomic-machine.h: Likewise.
	* sysdeps/arm/atomic-machine.h: Likewise.
	* sysdeps/i386/atomic-machine.h: Likewise.
	* sysdeps/ia64/atomic-machine.h: Likewise.
	* sysdeps/m68k/coldfire/atomic-machine.h: Likewise.
	* sysdeps/m68k/m680x0/m68020/atomic-machine.h: Likewise.
	* sysdeps/microblaze/atomic-machine.h: Likewise.
	* sysdeps/mips/atomic-machine.h: Likewise.
	* sysdeps/powerpc/powerpc32/atomic-machine.h: Likewise.
	* sysdeps/powerpc/powerpc64/atomic-machine.h: Likewise.
	* sysdeps/s390/atomic-machine.h: Likewise.
	* sysdeps/sparc/sparc32/atomic-machine.h: Likewise.
	* sysdeps/sparc/sparc32/sparcv9/atomic-machine.h: Likewise.
	* sysdeps/sparc/sparc64/atomic-machine.h: Likewise.
	* sysdeps/tile/tilegx/atomic-machine.h: Likewise.
	* sysdeps/tile/tilepro/atomic-machine.h: Likewise.
	* sysdeps/unix/sysv/linux/hppa/atomic-machine.h: Likewise.
	* sysdeps/unix/sysv/linux/m68k/coldfire/atomic-machine.h: Likewise.
	* sysdeps/unix/sysv/linux/nios2/atomic-machine.h: Likewise.
	* sysdeps/unix/sysv/linux/sh/atomic-machine.h: Likewise.
	* sysdeps/x86_64/atomic-machine.h: Likewise.
2017-06-06 09:41:56 +02:00
argp
assert
benchtests benchtests: Add more tests for memrchr 2017-06-04 09:45:09 -07:00
bits Define SIG_HOLD for XPG4 (bug 21538). 2017-06-05 10:19:03 +00:00
catgets
conform conformtest: Correct signal.h expectations for XPG4 / XPG42. 2017-06-01 17:17:43 +00:00
crypt
csu Delay initialization of CPU features struct in static binaries 2017-05-31 06:38:33 +05:30
ctype
debug Fix struct sigaltstack namespace (bug 21517). 2017-06-05 10:17:46 +00:00
dirent
dlfcn
elf Make __tunables_init hidden and avoid PLT 2017-05-25 06:55:58 -07:00
gmon
gnulib
grp
gshadow
hesiod
hurd Fix struct sigaltstack namespace (bug 21517). 2017-06-05 10:17:46 +00:00
iconv
iconvdata
include Optimize generic spinlock code and use C11 like atomic macros. 2017-06-06 09:41:56 +02:00
inet Remove __need macros from signal.h. 2017-05-20 19:04:43 -04:00
intl Suppress internal declarations for most of the testsuite. 2017-05-11 19:27:59 -04:00
io Remove __need macros from signal.h. 2017-05-20 19:04:43 -04:00
libidn
libio libio: Avoid dup already opened file descriptor [BZ#21393] 2017-05-22 18:13:35 -03:00
locale
localedata
login Remove __need macros from signal.h. 2017-05-20 19:04:43 -04:00
mach
malloc Add internal facility for dynamic array handling 2017-06-02 11:59:28 +02:00
manual manual: Provide consistent errno documentation. 2017-06-02 13:49:20 -07:00
math float128: Add wrappers to override ldbl-128 as float128. 2017-05-25 09:01:37 -03:00
mathvec
misc posix: Add missing build flags for p{write,read}v2 2017-06-02 11:12:29 -03:00
nis Include shlib-compat.h in many sunrpc/nis source files. 2017-06-04 11:31:28 -04:00
nptl Optimize generic spinlock code and use C11 like atomic macros. 2017-06-06 09:41:56 +02:00
nptl_db
nscd
nss Suppress internal declarations for most of the testsuite. 2017-05-11 19:27:59 -04:00
po
posix Remove __need macros from signal.h. 2017-05-20 19:04:43 -04:00
pwd
resolv Include shlib-compat.h in many sunrpc/nis source files. 2017-06-04 11:31:28 -04:00
resource
rt Remove __need macros from signal.h. 2017-05-20 19:04:43 -04:00
scripts Also create and use ldbl-compat-choose.h. 2017-05-19 11:30:26 +00:00
setjmp Remove __need macros from signal.h. 2017-05-20 19:04:43 -04:00
shadow Remove __need macros from signal.h. 2017-05-20 19:04:43 -04:00
signal Fix struct sigaltstack namespace (bug 21517). 2017-06-05 10:17:46 +00:00
socket Remove __need macros from signal.h. 2017-05-20 19:04:43 -04:00
soft-fp
stdio-common
stdlib Include sys/param.h in stdlib/gmp-impl.h instead of redefining MAX/MIN 2017-06-01 20:44:22 -03:00
streams
string Add memchr tests for n == 0 2017-05-25 11:38:01 -07:00
sunrpc Include shlib-compat.h in many sunrpc/nis source files. 2017-06-04 11:31:28 -04:00
support resolv: Tests for various versions of res_init 2017-06-02 15:50:36 +02:00
sysdeps Optimize generic spinlock code and use C11 like atomic macros. 2017-06-06 09:41:56 +02:00
sysvipc
termios
time
timezone
wcsmbs
wctype
.gitattributes
.gitignore
abi-tags Remove the bulk of the NaCl port. 2017-05-20 08:09:10 -04:00
aclocal.m4
BUGS
ChangeLog Optimize generic spinlock code and use C11 like atomic macros. 2017-06-06 09:41:56 +02:00
ChangeLog.1
ChangeLog.2
ChangeLog.3
ChangeLog.4
ChangeLog.5
ChangeLog.6
ChangeLog.7
ChangeLog.8
ChangeLog.9
ChangeLog.10
ChangeLog.11
ChangeLog.12
ChangeLog.13
ChangeLog.14
ChangeLog.15
ChangeLog.16
ChangeLog.17
ChangeLog.old-ports
ChangeLog.old-ports-aarch64
ChangeLog.old-ports-aix
ChangeLog.old-ports-alpha
ChangeLog.old-ports-am33
ChangeLog.old-ports-arm
ChangeLog.old-ports-cris
ChangeLog.old-ports-hppa
ChangeLog.old-ports-ia64
ChangeLog.old-ports-linux-generic
ChangeLog.old-ports-m68k
ChangeLog.old-ports-microblaze
ChangeLog.old-ports-mips
ChangeLog.old-ports-powerpc
ChangeLog.old-ports-tile
config.h.in Suppress internal declarations for most of the testsuite. 2017-05-11 19:27:59 -04:00
config.make.in
configure
configure.ac
CONFORMANCE
COPYING
COPYING.LIB
extra-lib.mk
gen-locales.mk
INSTALL
libc-abis
libof-iterator.mk
LICENSES
MAINTAINERS Add MAINTAINERS 2017-05-11 13:38:30 -04:00
Makeconfig Support dl-tunables.list in subdirectories 2017-05-25 05:41:18 -07:00
Makefile Suppress internal declarations for most of the testsuite. 2017-05-11 19:27:59 -04:00
Makefile.in
Makerules Also create and use ldbl-compat-choose.h. 2017-05-19 11:30:26 +00:00
NAMESPACE
NEWS Optimize generic spinlock code and use C11 like atomic macros. 2017-06-06 09:41:56 +02:00
o-iterator.mk
README
README.pretty-printers
README.tunables tunables: Add support for tunables of uint64_t type 2017-05-17 13:11:55 +05:30
Rules Suppress internal declarations for most of the testsuite. 2017-05-11 19:27:59 -04:00
shlib-versions
test-skeleton.c
version.h
WUR-REPORT

This directory contains the sources of the GNU C Library.
See the file "version.h" for what release version you have.

The GNU C Library is the standard system C library for all GNU systems,
and is an important part of what makes up a GNU system.  It provides the
system API for all programs written in C and C-compatible languages such
as C++ and Objective C; the runtime facilities of other programming
languages use the C library to access the underlying operating system.

In GNU/Linux systems, the C library works with the Linux kernel to
implement the operating system behavior seen by user applications.
In GNU/Hurd systems, it works with a microkernel and Hurd servers.

The GNU C Library implements much of the POSIX.1 functionality in the
GNU/Hurd system, using configurations i[4567]86-*-gnu.  The current
GNU/Hurd support requires out-of-tree patches that will eventually be
incorporated into an official GNU C Library release.

When working with Linux kernels, this version of the GNU C Library
requires Linux kernel version 3.2 or later.

Also note that the shared version of the libgcc_s library must be
installed for the pthread library to work correctly.

The GNU C Library supports these configurations for using Linux kernels:

	aarch64*-*-linux-gnu
	alpha*-*-linux-gnu
	arm-*-linux-gnueabi
	hppa-*-linux-gnu	Not currently functional without patches.
	i[4567]86-*-linux-gnu
	x86_64-*-linux-gnu	Can build either x86_64 or x32
	ia64-*-linux-gnu
	m68k-*-linux-gnu
	microblaze*-*-linux-gnu
	mips-*-linux-gnu
	mips64-*-linux-gnu
	powerpc-*-linux-gnu	Hardware or software floating point, BE only.
	powerpc64*-*-linux-gnu	Big-endian and little-endian.
	s390-*-linux-gnu
	s390x-*-linux-gnu
	sh[34]-*-linux-gnu
	sparc*-*-linux-gnu
	sparc64*-*-linux-gnu
	tilegx-*-linux-gnu
	tilepro-*-linux-gnu

If you are interested in doing a port, please contact the glibc
maintainers; see http://www.gnu.org/software/libc/ for more
information.

See the file INSTALL to find out how to configure, build, and install
the GNU C Library.  You might also consider reading the WWW pages for
the C library at http://www.gnu.org/software/libc/.

The GNU C Library is (almost) completely documented by the Texinfo manual
found in the `manual/' subdirectory.  The manual is still being updated
and contains some known errors and omissions; we regret that we do not
have the resources to work on the manual as much as we would like.  For
corrections to the manual, please file a bug in the `manual' component,
following the bug-reporting instructions below.  Please be sure to check
the manual in the current development sources to see if your problem has
already been corrected.

Please see http://www.gnu.org/software/libc/bugs.html for bug reporting
information.  We are now using the Bugzilla system to track all bug reports.
This web page gives detailed information on how to report bugs properly.

The GNU C Library is free software.  See the file COPYING.LIB for copying
conditions, and LICENSES for notices about a few contributions that require
these additional notices to be distributed.  License copyright years may be
listed using range notation, e.g., 1996-2015, indicating that every year in
the range, inclusive, is a copyrightable year that would otherwise be listed
individually.