RFC: Always-on elision with per-process opt-in using tunables.
Stefan Liebler
stli@linux.vnet.ibm.com
Wed Jun 21 07:02:00 GMT 2017
Are there any news for this?
On 05/12/2017 01:13 PM, Stefan Liebler wrote:
> 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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