RFC: Always-on elision with per-process opt-in using tunables.
Stefan Liebler
stli@linux.vnet.ibm.com
Fri May 12 11:14:00 GMT 2017
On 05/11/2017 05:45 PM, Carlos O'Donell wrote:
> I am going to propose the following:
>
> * Always build with elision support.
>
> * Elision disabled by default at runtime.
>
> * Use tunables to allow processes to opt-in to transparent elision.
>
> The benefit is that the elision support doesn't bit-rot, and we keep
> it working, and that distributions can conservatively backport elision
> and allow users to test enablement on a per-process basis.
This is an improvement for users as they can simply compare performance
of their workload with or without lock elsion.
With (c) - see below - further tuning is possible.
>
> The elision is enabled with:
>
> GLIBC_TUNABLE=glibc.elision.enable=1
>
> The obvious set of patches are:
>
> (a) Split out some cleanups in this patch.
> (b) Always build with elision and us tunables to opt-in.
> (c) Extend tunables to allow modification of elision parameters
> (useful for upcoming rwlock elision re-enablement).
>
> I'm testing this on x86_64, ppc64le, and s390x.
>
I've applied this patch to test on s390x.
Some changes are needed in order to build it.
Please remove the line "enable-lock-elision = @enable_lock_elision"
in config.make.in. This variable is used in
sysdeps/unix/sysv/linux/s390/Makefile, which has to be adjusted, too:
ifeq ($(enable-lock-elision),yes)
...
endif
The s390 configure check to test the availability of __builtin_tbegin
has to be adjusted:
diff --git a/sysdeps/s390/configure.ac b/sysdeps/s390/configure.ac
index 8a782e7..62bcfb9 100644
--- a/sysdeps/s390/configure.ac
+++ b/sysdeps/s390/configure.ac
@@ -32,7 +32,7 @@ else
fi
rm -f conftest* ])
-if test "$enable_lock_elision" = yes && test
"$libc_cv_gcc_builtin_tbegin" = no ; then
+if test "$libc_cv_gcc_builtin_tbegin" = no ; then
critic_missing="$critic_missing The used GCC has no support for
__builtin_tbegin, which is needed for lock-elision on target S390."
fi
Note: __builtin_tbegin is available on RHEL/SLES GCC 4.8.5.
Please remove '--enable-lock-elision=yes' in INSTALL, too.
With these mentioned changes and the comments below,
I could build glibc and the testsuite runs without regressions.
I've also used a small s390 specific test program to check wether a
mutex was elided or not:
./prog
Lock was a normal lock!
GLIBC_TUNABLES=glibc.elision.enable=0 ./prog
Lock was a normal lock!
GLIBC_TUNABLES=glibc.elision.enable=1 ./prog
Lock was elided via a transaction! (nesting-depth=1)
GLIBC_TUNABLES=glibc.elision.enable=1 ./prog_secure
Lock was a normal lock!
GLIBC_TUNABLES=glibc.elision.enable=2 ./prog
Lock was a normal lock!
GLIBC_TUNABLES=glibc.elision.enable=yes ./prog
Lock was a normal lock!
> Thoughts?
>
> diff --git a/config.h.in b/config.h.in
> index 2caa412..47b139e 100644
> --- a/config.h.in
> +++ b/config.h.in
> @@ -147,9 +147,6 @@
> /* Define if __stack_chk_guard canary should be randomized at program startup. */
> #undef ENABLE_STACKGUARD_RANDOMIZE
>
> -/* Define if lock elision should be enabled by default. */
> -#undef ENABLE_LOCK_ELISION
> -
> /* Package description. */
> #undef PKGVERSION
>
> diff --git a/configure b/configure
> index 422482f..d3b68c1 100755
> --- a/configure
> +++ b/configure
> @@ -677,7 +677,6 @@ enable_werror
> all_warnings
> force_install
> bindnow
> -enable_lock_elision
> hardcoded_path_in_tests
> enable_timezone_tools
> use_default_link
> @@ -766,7 +765,6 @@ enable_profile
> enable_timezone_tools
> enable_hardcoded_path_in_tests
> enable_stackguard_randomization
> -enable_lock_elision
> enable_add_ons
> enable_hidden_plt
> enable_bind_now
> @@ -1427,8 +1425,6 @@ Optional Features:
> --enable-stackguard-randomization
> initialize __stack_chk_guard canary with a random
> number at program start
> - --enable-lock-elision=yes/no
> - Enable lock elision for pthread mutexes by default
> --enable-add-ons[=DIRS...]
> configure and build add-ons in DIR1,DIR2,... search
> for add-ons if no parameter given
> @@ -3395,19 +3391,6 @@ if test "$enable_stackguard_randomize" = yes; then
>
> fi
>
> -# Check whether --enable-lock-elision was given.
> -if test "${enable_lock_elision+set}" = set; then :
> - enableval=$enable_lock_elision; enable_lock_elision=$enableval
> -else
> - enable_lock_elision=no
> -fi
> -
> -
> -if test "$enable_lock_elision" = yes ; then
> - $as_echo "#define ENABLE_LOCK_ELISION 1" >>confdefs.h
> -
> -fi
> -
> # Check whether --enable-add-ons was given.
> if test "${enable_add_ons+set}" = set; then :
> enableval=$enable_add_ons;
> diff --git a/configure.ac b/configure.ac
> index 7f43042..a970296 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -199,16 +199,6 @@ if test "$enable_stackguard_randomize" = yes; then
> AC_DEFINE(ENABLE_STACKGUARD_RANDOMIZE)
> fi
>
> -AC_ARG_ENABLE([lock-elision],
> - AC_HELP_STRING([--enable-lock-elision[=yes/no]],
> - [Enable lock elision for pthread mutexes by default]),
> - [enable_lock_elision=$enableval],
> - [enable_lock_elision=no])
> -AC_SUBST(enable_lock_elision)
> -if test "$enable_lock_elision" = yes ; then
> - AC_DEFINE(ENABLE_LOCK_ELISION)
> -fi
> -
> dnl Generic infrastructure for drop-in additions to libc.
> AC_ARG_ENABLE([add-ons],
> AC_HELP_STRING([--enable-add-ons@<:@=DIRS...@:>@],
> diff --git a/elf/dl-tunables.h b/elf/dl-tunables.h
> index f33adfb..3dad518 100644
> --- a/elf/dl-tunables.h
> +++ b/elf/dl-tunables.h
> @@ -18,8 +18,8 @@
> License along with the GNU C Library; if not, see
> <http://www.gnu.org/licenses/>. */
>
> -#ifndef _TUNABLES_H_
> -#define _TUNABLES_H_
> +#ifndef _DL_TUNABLES_H_
> +#define _DL_TUNABLES_H_
>
> #if !HAVE_TUNABLES
> static inline void
> diff --git a/elf/dl-tunables.list b/elf/dl-tunables.list
> index b9f1488..97062f9 100644
> --- a/elf/dl-tunables.list
> +++ b/elf/dl-tunables.list
> @@ -77,4 +77,12 @@ glibc {
> security_level: SXID_IGNORE
> }
> }
> + elision {
> + enable {
> + type: INT_32
> + minval: 0
> + maxval: 1
> + security_level: SXID_IGNORE
> + }
> + }
> }
> diff --git a/nptl/Makefile b/nptl/Makefile
> index 6d48c0c..a720612 100644
> --- a/nptl/Makefile
> +++ b/nptl/Makefile
> @@ -704,6 +704,10 @@ $(objpfx)tst-oddstacklimit.out: $(objpfx)tst-oddstacklimit $(objpfx)tst-basic1
> $(evaluate-test)
> endif
>
> +# Disable elision for tst-mutex8 so it can verify error case for
> +# destroying a mutex.
> +tst-mutex8-ENV = GLIBC_TUNABLES=glibc.elision.enable=0
> +
> # The tests here better do not run in parallel
> ifneq ($(filter %tests,$(MAKECMDGOALS)),)
> .NOTPARALLEL:
> diff --git a/nptl/tst-mutex8.c b/nptl/tst-mutex8.c
> index 1d288d2..ef59db5 100644
> --- a/nptl/tst-mutex8.c
> +++ b/nptl/tst-mutex8.c
> @@ -127,9 +127,8 @@ check_type (const char *mas, pthread_mutexattr_t *ma)
> return 1;
> }
>
> - /* Elided mutexes don't fail destroy. If elision is not explicitly disabled
> - we don't know, so can also not check this. */
> -#ifndef ENABLE_LOCK_ELISION
> + /* Elided mutexes don't fail destroy, but this test is run with
> + elision disabled so we can test them. */
> e = pthread_mutex_destroy (m);
> if (e == 0)
> {
> @@ -142,7 +141,6 @@ check_type (const char *mas, pthread_mutexattr_t *ma)
> mas);
> return 1;
> }
> -#endif
>
> if (pthread_mutex_unlock (m) != 0)
> {
> @@ -157,7 +155,6 @@ check_type (const char *mas, pthread_mutexattr_t *ma)
> }
>
> /* Elided mutexes don't fail destroy. */
> -#ifndef ENABLE_LOCK_ELISION
> e = pthread_mutex_destroy (m);
> if (e == 0)
> {
> @@ -171,7 +168,6 @@ mutex_destroy of self-trylocked mutex did not return EBUSY %s\n",
> mas);
> return 1;
> }
> -#endif
>
> if (pthread_mutex_unlock (m) != 0)
> {
> @@ -207,7 +203,6 @@ mutex_destroy of self-trylocked mutex did not return EBUSY %s\n",
> }
>
> /* Elided mutexes don't fail destroy. */
> -#ifndef ENABLE_LOCK_ELISION
> e = pthread_mutex_destroy (m);
> if (e == 0)
> {
> @@ -220,7 +215,6 @@ mutex_destroy of self-trylocked mutex did not return EBUSY %s\n",
> mutex_destroy of condvar-used mutex did not return EBUSY for %s\n", mas);
> return 1;
> }
> -#endif
>
> done = true;
> if (pthread_cond_signal (&c) != 0)
> @@ -280,7 +274,6 @@ mutex_destroy of condvar-used mutex did not return EBUSY for %s\n", mas);
> }
>
> /* Elided mutexes don't fail destroy. */
> -#ifndef ENABLE_LOCK_ELISION
> e = pthread_mutex_destroy (m);
> if (e == 0)
> {
> @@ -295,7 +288,6 @@ mutex_destroy of condvar-used mutex did not return EBUSY for %s\n", mas);
> mas);
> return 1;
> }
> -#endif
>
> if (pthread_cancel (th) != 0)
> {
> diff --git a/scripts/gen-tunables.awk b/scripts/gen-tunables.awk
> index 601240a..6dba7e1 100644
> --- a/scripts/gen-tunables.awk
> +++ b/scripts/gen-tunables.awk
> @@ -122,9 +122,9 @@ END {
> }
>
> print "/* AUTOGENERATED by gen-tunables.awk. */"
> - print "#ifndef _TUNABLES_H_"
> + print "#ifndef _DL_TUNABLES_H_"
> print "# error \"Do not include this file directly.\""
> - print "# error \"Include tunables.h instead.\""
> + print "# error \"Include dl-tunables.h instead.\""
> print "#endif"
>
> # Now, the enum names
> diff --git a/sysdeps/powerpc/nptl/elide.h b/sysdeps/powerpc/nptl/elide.h
> index 1c42814..06986cc 100644
> --- a/sysdeps/powerpc/nptl/elide.h
> +++ b/sysdeps/powerpc/nptl/elide.h
> @@ -19,7 +19,6 @@
> #ifndef ELIDE_PPC_H
> # define ELIDE_PPC_H
>
> -#ifdef ENABLE_LOCK_ELISION
> # include <htm.h>
> # include <elision-conf.h>
>
> @@ -114,12 +113,4 @@ __elide_unlock (int is_lock_free)
> # define ELIDE_UNLOCK(is_lock_free) \
> __elide_unlock (is_lock_free)
>
> -# else
> -
> -# define ELIDE_LOCK(adapt_count, is_lock_free) 0
> -# define ELIDE_TRYLOCK(adapt_count, is_lock_free, write) 0
> -# define ELIDE_UNLOCK(is_lock_free) 0
> -
> -#endif /* ENABLE_LOCK_ELISION */
> -
> #endif
> diff --git a/sysdeps/powerpc/powerpc32/sysdep.h b/sysdeps/powerpc/powerpc32/sysdep.h
> index f92ab2c..0ed83d3 100644
> --- a/sysdeps/powerpc/powerpc32/sysdep.h
> +++ b/sysdeps/powerpc/powerpc32/sysdep.h
> @@ -88,7 +88,7 @@ GOT_LABEL: ; \
> cfi_endproc; \
> ASM_SIZE_DIRECTIVE(name)
>
> -#if ! IS_IN(rtld) && defined (ENABLE_LOCK_ELISION)
> +#if ! IS_IN(rtld)
> # define ABORT_TRANSACTION \
> cmpwi 2,0; \
> beq 1f; \
> diff --git a/sysdeps/powerpc/powerpc64/sysdep.h b/sysdeps/powerpc/powerpc64/sysdep.h
> index db7c1d7..79a2697 100644
> --- a/sysdeps/powerpc/powerpc64/sysdep.h
> +++ b/sysdeps/powerpc/powerpc64/sysdep.h
> @@ -272,7 +272,7 @@ LT_LABELSUFFIX(name,_name_end): ; \
> TRACEBACK_MASK(name,mask) \
> END_2(name)
>
> -#if !IS_IN(rtld) && defined (ENABLE_LOCK_ELISION)
> +#if !IS_IN(rtld)
> # define ABORT_TRANSACTION \
> cmpdi 13,0; \
> beq 1f; \
> diff --git a/sysdeps/powerpc/sysdep.h b/sysdeps/powerpc/sysdep.h
> index f07b959..d1a9bd9 100644
> --- a/sysdeps/powerpc/sysdep.h
> +++ b/sysdeps/powerpc/sysdep.h
> @@ -21,10 +21,8 @@
> */
> #define _SYSDEPS_SYSDEP_H 1
> #include <bits/hwcap.h>
> -#ifdef ENABLE_LOCK_ELISION
> #include <tls.h>
> #include <htm.h>
> -#endif
>
> #define PPC_FEATURE_970 (PPC_FEATURE_POWER4 + PPC_FEATURE_HAS_ALTIVEC)
>
> @@ -176,7 +174,7 @@
> we abort transaction just before syscalls.
>
> [1] Documentation/powerpc/transactional_memory.txt [Syscalls] */
> -#if !IS_IN(rtld) && defined (ENABLE_LOCK_ELISION)
> +#if !IS_IN(rtld)
> # define ABORT_TRANSACTION \
> ({ \
> if (THREAD_GET_TM_CAPABLE ()) \
> diff --git a/sysdeps/s390/nptl/bits/pthreadtypes.h b/sysdeps/s390/nptl/bits/pthreadtypes.h
> index 48ffdb4..88d21f0 100644
> --- a/sysdeps/s390/nptl/bits/pthreadtypes.h
> +++ b/sysdeps/s390/nptl/bits/pthreadtypes.h
> @@ -89,37 +89,25 @@ typedef union
> binary compatibility with static initializers. */
> int __kind;
> #if __WORDSIZE == 64
> -# ifdef ENABLE_LOCK_ELISION
> short __spins;
> short __elision;
> /* Mutex __spins initializer used by PTHREAD_MUTEX_INITIALIZER. */
> -# define __PTHREAD_SPINS 0, 0
> -# else
> - int __spins;
> - /* Mutex __spins initializer used by PTHREAD_MUTEX_INITIALIZER. */
> -# define __PTHREAD_SPINS 0
> -# endif
> +# define __PTHREAD_SPINS 0, 0
> __pthread_list_t __list;
> # define __PTHREAD_MUTEX_HAVE_PREV 1
> #else
> unsigned int __nusers;
> __extension__ union
> {
> -# ifdef ENABLE_LOCK_ELISION
> struct
> {
> short __espins;
> short __elision;
> } _d;
> -# define __spins _d.__espins
> -# define __elision _d.__elision
> - /* Mutex __spins initializer used by PTHREAD_MUTEX_INITIALIZER. */
> -# define __PTHREAD_SPINS { 0, 0 }
> -# else
> - int __spins;
> - /* Mutex __spins initializer used by PTHREAD_MUTEX_INITIALIZER. */
> -# define __PTHREAD_SPINS 0
> -# endif
> +# define __spins _d.__espins
> +# define __elision _d.__elision
> + /* Mutex __spins initializer used by PTHREAD_MUTEX_INITIALIZER. */
> +# define __PTHREAD_SPINS { 0, 0 }
> __pthread_slist_t __list;
> };
> #endif
Adhemerval's commit "Move shared pthread definitions to common headers"
consolidates the pthradtypes.h files.
Thus sysdeps/s390/nptl/bits/pthreadtypes.h does not exist anymore.
I've adjusted sysdeps/s390/nptl/bits/pthreadtypes-arch.h for my test:
diff --git a/sysdeps/s390/nptl/bits/pthreadtypes-arch.h
b/sysdeps/s390/nptl/bits/pthreadtypes-arch.h
index 3a9ac57..db7195a 100644
--- a/sysdeps/s390/nptl/bits/pthreadtypes-arch.h
+++ b/sysdeps/s390/nptl/bits/pthreadtypes-arch.h
@@ -40,11 +40,7 @@
/* Definitions for internal mutex struct. */
#define __PTHREAD_COMPAT_PADDING_MID
#define __PTHREAD_COMPAT_PADDING_END
-#ifdef ENABLE_LOCK_ELISION
#define __PTHREAD_MUTEX_LOCK_ELISION 1
-#else
-#define __PTHREAD_MUTEX_LOCK_ELISION 0
-#endif
#define __LOCK_ALIGNMENT
#define __ONCE_ALIGNMENT
> diff --git a/sysdeps/unix/sysv/linux/powerpc/elision-conf.c b/sysdeps/unix/sysv/linux/powerpc/elision-conf.c
> index f631f0a..a767a0c 100644
> --- a/sysdeps/unix/sysv/linux/powerpc/elision-conf.c
> +++ b/sysdeps/unix/sysv/linux/powerpc/elision-conf.c
> @@ -21,6 +21,7 @@
> #include <elision-conf.h>
> #include <unistd.h>
> #include <dl-procinfo.h>
> +#include <elf/dl-tunables.h>
>
> /* Reasonable initial tuning values, may be revised in the future.
> This is a conservative initial value. */
> @@ -54,18 +55,47 @@ int __pthread_force_elision attribute_hidden;
>
> /* Initialize elision. */
>
> +static inline void
> +do_set_elision_enable (bool elision_enable)
> +{
> + /* If elision is not enabled, or we are in a secure mode,
> + make sure elision is never used... */
> + if (!elision_enable || __libc_enable_secure)
> + {
> + __pthread_force_elision = 0;
> + return;
> + }
> +
> + /* ... otherwise enable elision based on hardare availability. */
> + __pthread_force_elision = (GLRO (dl_hwcap2)
> + & PPC_FEATURE2_HAS_HTM) ? 1 : 0;
> +}
> +
> +#if HAVE_TUNABLES
> +/* The elision->enable tunable is either 0 or 1 to indicate that
> + elision should be disabled or enabled respectively. Availability at
> + the hardware level will still dictate if the feature is used. */
> +void
> +DL_TUNABLE_CALLBACK (set_elision_enable) (tunable_val_t *elision_enable)
tunable_val_t *valp instead of tunable_val_t *elision_enable.
> +{
> + int32_t elision_enable = (int32_t) valp->numval;
> + do_set_elision_enable (elision_enable ? true : false);
> +}
> +#endif
> +
> static void
> elision_init (int argc __attribute__ ((unused)),
> char **argv __attribute__ ((unused)),
> char **environ)
> {
> -#ifdef ENABLE_LOCK_ELISION
> - int elision_available = (GLRO (dl_hwcap2) & PPC_FEATURE2_HAS_HTM) ? 1 : 0;
> - __pthread_force_elision = __libc_enable_secure ? 0 : elision_available;
> +#if HAVE_TUNABLES
> + /* Elision depends on tunables to enable and tune elision at runtime. */
> +# define TUNABLE_NAMESPACE elision
> + TUNABLE_SET_VAL_WITH_CALLBACK (enable, NULL, set_elision_enable);
> +#else
> + /* Disable elision when built without tunables. */
> + do_set_elision_enable (false);
> #endif
> - if (!__pthread_force_elision)
> - /* Disable elision on rwlocks. */
> - __elision_aconf.try_tbegin = 0;
> }
>
> #ifdef SHARED
> diff --git a/sysdeps/unix/sysv/linux/powerpc/force-elision.h b/sysdeps/unix/sysv/linux/powerpc/force-elision.h
> index 318f791..d1feeeb 100644
> --- a/sysdeps/unix/sysv/linux/powerpc/force-elision.h
> +++ b/sysdeps/unix/sysv/linux/powerpc/force-elision.h
> @@ -16,7 +16,6 @@
> License along with the GNU C Library; if not, see
> <http://www.gnu.org/licenses/>. */
>
> -#ifdef ENABLE_LOCK_ELISION
> /* Automatically enable elision for existing user lock kinds. */
> #define FORCE_ELISION(m, s) \
> if (__pthread_force_elision \
> @@ -25,4 +24,3 @@
> mutex->__data.__kind |= PTHREAD_MUTEX_ELISION_NP; \
> s; \
> }
> -#endif
> diff --git a/sysdeps/unix/sysv/linux/s390/elision-conf.c b/sysdeps/unix/sysv/linux/s390/elision-conf.c
> index cc0fdef..c6d9962 100644
> --- a/sysdeps/unix/sysv/linux/s390/elision-conf.c
> +++ b/sysdeps/unix/sysv/linux/s390/elision-conf.c
> @@ -21,6 +21,7 @@
> #include <elision-conf.h>
> #include <unistd.h>
> #include <dl-procinfo.h>
> +#include <elf/dl-tunables.h>
>
> /* Reasonable initial tuning values, may be revised in the future.
> This is a conservative initial value. */
> @@ -55,16 +56,46 @@ int __pthread_force_elision attribute_hidden = 0;
>
> /* Initialize elison. */
>
> +static inline void
> +do_set_elision_enable (bool elision_enable)
> +{
> + /* If elision is not enabled, or we are in a secure mode,
> + make sure elision is never used... */
> + if (!elision_enable || __libc_enable_secure)
> + {
> + __pthread_force_elision = 0;
> + return;
> + }
> +
> + /* ... otherwise enable elision based on hardare availability. */
> + __pthread_force_elision = (GLRO (dl_hwcap) & HWCAP_S390_TE) ? 1 : 0;
> +}
> +
> +#if HAVE_TUNABLES
> +/* The elision->enable tunable is either 0 or 1 to indicate that
> + elision should be disabled or enabled respectively. Availability at
> + the hardware level will still dictate if the feature is used. */
> +void
> +DL_TUNABLE_CALLBACK (set_elision_enable) (tunable_val_t *elision_enable)
tunable_val_t *valp instead of tunable_val_t *elision_enable.
> +{
> + int32_t elision_enable = (int32_t) valp->numval;
> + do_set_elision_enable (elision_enable ? true : false);
> +}
> +#endif
> +
> static void
> elision_init (int argc __attribute__ ((unused)),
> char **argv __attribute__ ((unused)),
> char **environ)
> {
> - /* Set when the CPU and the kernel supports transactional execution.
> - When false elision is never attempted. */
> - int elision_available = (GLRO (dl_hwcap) & HWCAP_S390_TE) ? 1 : 0;
> -
> - __pthread_force_elision = __libc_enable_secure ? 0 : elision_available;
> +#if HAVE_TUNABLES
> + /* Elision depends on tunables to enable and tune elision at runtime. */
> +# define TUNABLE_NAMESPACE elision
> + TUNABLE_SET_VAL_WITH_CALLBACK (enable, NULL, set_elision_enable);
> +#else
> + /* Disable elision when built without tunables. */
> + do_set_elision_enable (false);
> +#endif
> }
>
> #ifdef SHARED
> diff --git a/sysdeps/unix/sysv/linux/s390/elision-conf.h b/sysdeps/unix/sysv/linux/s390/elision-conf.h
> index 3143f3b..32f0ed3 100644
> --- a/sysdeps/unix/sysv/linux/s390/elision-conf.h
> +++ b/sysdeps/unix/sysv/linux/s390/elision-conf.h
> @@ -15,7 +15,6 @@
> You should have received a copy of the GNU Lesser General Public
> License along with the GNU C Library; if not, see
> <http://www.gnu.org/licenses/>. */
> -#ifdef ENABLE_LOCK_ELISION
> #ifndef _ELISION_CONF_H
> #define _ELISION_CONF_H 1
>
> @@ -41,4 +40,3 @@ extern int __pthread_force_elision attribute_hidden;
> #define HAVE_ELISION 1
>
> #endif
> -#endif
> diff --git a/sysdeps/unix/sysv/linux/s390/force-elision.h b/sysdeps/unix/sysv/linux/s390/force-elision.h
> index 3ae3bcd..8e1e33e 100644
> --- a/sysdeps/unix/sysv/linux/s390/force-elision.h
> +++ b/sysdeps/unix/sysv/linux/s390/force-elision.h
> @@ -16,7 +16,6 @@
> License along with the GNU C Library; if not, see
> <http://www.gnu.org/licenses/>. */
>
> -#ifdef ENABLE_LOCK_ELISION
> /* Automatically enable elision for existing user lock kinds. */
> #define FORCE_ELISION(m, s) \
> if (__pthread_force_elision \
> @@ -25,4 +24,3 @@
> mutex->__data.__kind |= PTHREAD_MUTEX_ELISION_NP; \
> s; \
> }
> -#endif
> diff --git a/sysdeps/unix/sysv/linux/s390/lowlevellock.h b/sysdeps/unix/sysv/linux/s390/lowlevellock.h
> index 604137f..48f87a8 100644
> --- a/sysdeps/unix/sysv/linux/s390/lowlevellock.h
> +++ b/sysdeps/unix/sysv/linux/s390/lowlevellock.h
> @@ -22,7 +22,6 @@
> #include <sysdeps/nptl/lowlevellock.h>
>
> /* Transactional lock elision definitions. */
> -# ifdef ENABLE_LOCK_ELISION
> extern int __lll_timedlock_elision
> (int *futex, short *adapt_count, const struct timespec *timeout, int private)
> attribute_hidden;
> @@ -45,6 +44,5 @@ extern int __lll_trylock_elision(int *futex, short *adapt_count)
> __lll_unlock_elision (&(futex), &(adapt_count), private)
> # define lll_trylock_elision(futex, adapt_count) \
Can you adjust the occurences of "# define" within the old #ifdef
ENABLE_LOCK_ELISON block to "# define".
> __lll_trylock_elision(&(futex), &(adapt_count))
> -# endif /* ENABLE_LOCK_ELISION */
>
> #endif /* lowlevellock.h */
> diff --git a/sysdeps/unix/sysv/linux/x86/elision-conf.c b/sysdeps/unix/sysv/linux/x86/elision-conf.c
> index 673b000..7d3d8fd 100644
> --- a/sysdeps/unix/sysv/linux/x86/elision-conf.c
> +++ b/sysdeps/unix/sysv/linux/x86/elision-conf.c
> @@ -21,6 +21,7 @@
> #include <init-arch.h>
> #include <elision-conf.h>
> #include <unistd.h>
> +#include <elf/dl-tunables.h>
>
> /* Reasonable initial tuning values, may be revised in the future.
> This is a conservative initial value. */
> @@ -52,17 +53,46 @@ int __pthread_force_elision attribute_hidden;
>
> /* Initialize elison. */
>
> +static inline void
> +do_set_elision_enable (bool elision_enable)
> +{
> + /* If elision is not enabled, or we are in a secure mode,
> + make sure elision is never used... */
> + if (!elision_enable || __libc_enable_secure)
> + {
> + __pthread_force_elision = 0;
> + return;
> + }
> +
> + /* ... otherwise enable elision based on hardare availability. */
> + __pthread_force_elision = HAS_CPU_FEATURE (RTM);
> +}
> +
> +#if HAVE_TUNABLES
> +/* The elision->enable tunable is either 0 or 1 to indicate that
> + elision should be disabled or enabled respectively. Availability at
> + the hardware level will still dictate if the feature is used. */
> +void
> +DL_TUNABLE_CALLBACK (set_elision_enable) (tunable_val_t *valp)
> +{
> + int32_t elision_enable = (int32_t) valp->numval;
> + do_set_elision_enable (elision_enable ? true : false);
> +}
> +#endif
> +
> static void
> elision_init (int argc __attribute__ ((unused)),
> char **argv __attribute__ ((unused)),
> char **environ)
> {
> - int elision_available = HAS_CPU_FEATURE (RTM);
> -#ifdef ENABLE_LOCK_ELISION
> - __pthread_force_elision = __libc_enable_secure ? 0 : elision_available;
> +#if HAVE_TUNABLES
> + /* Elision depends on tunables to enable and tune elision at runtime. */
> +# define TUNABLE_NAMESPACE elision
> + TUNABLE_SET_VAL_WITH_CALLBACK (enable, NULL, set_elision_enable);
> +#else
> + /* Disable elision when built without tunables. */
> + do_set_elision_enable (false);
> #endif
> - if (!elision_available)
> - __elision_aconf.retry_try_xbegin = 0; /* Disable elision on rwlocks */
> }
>
> #ifdef SHARED
> ---
>
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