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f0458cf4f9
Linux from 3.9 through 4.2 does not abort HTM transaction on syscalls, instead it suspend and resume it when leaving the kernel. The side-effects of the syscall will always remain visible, even if the transaction is aborted. This is an issue when transaction is used along with futex syscall, on pthread_cond_wait for instance, where the futex call might succeed but the transaction is rolled back leading the pthread_cond object in an inconsistent state. Glibc used to prevent it by always aborting a transaction before issuing a syscall. Linux 4.2 also decided to abort active transaction in syscalls which makes the glibc workaround superfluous. Worse, glibc transaction abortion leads to a performance issue on recent kernels where the HTM state is saved/restore lazily (v4.9). By aborting a transaction on every syscalls, regardless whether a transaction has being initiated before, GLIBS makes the kernel always save/restore HTM state (it can not even lazily disable it after a certain number of syscall iterations). Because of this shortcoming, Transactional Lock Elision is just enabled when it has been explicitly set (either by tunables of by a configure switch) and if kernel aborts HTM transactions on syscalls (PPC_FEATURE2_HTM_NOSC). It is reported that using simple benchmark [1], the context-switch is about 5% faster by not issuing a tabort in every syscall in newer kernels. Checked on powerpc64le-linux-gnu with 4.4.0 kernel (Ubuntu 16.04). * NEWS: Add note about new TLE support on powerpc64le. * sysdeps/powerpc/nptl/tcb-offsets.sym (TM_CAPABLE): Remove. * sysdeps/powerpc/nptl/tls.h (tcbhead_t): Rename tm_capable to __ununsed1. (TLS_INIT_TP, TLS_DEFINE_INIT_TP): Remove tm_capable setup. (THREAD_GET_TM_CAPABLE, THREAD_SET_TM_CAPABLE): Remove macros. * sysdeps/powerpc/powerpc32/sysdep.h, sysdeps/powerpc/powerpc64/sysdep.h (ABORT_TRANSACTION_IMPL, ABORT_TRANSACTION): Remove macros. * sysdeps/powerpc/sysdep.h (ABORT_TRANSACTION): Likewise. * sysdeps/unix/sysv/linux/powerpc/elision-conf.c (elision_init): Set __pthread_force_elision iff PPC_FEATURE2_HTM_NOSC is set. * sysdeps/unix/sysv/linux/powerpc/powerpc32/sysdep.h, sysdeps/unix/sysv/linux/powerpc/powerpc64/sysdep.h sysdeps/unix/sysv/linux/powerpc/syscall.S (ABORT_TRANSACTION): Remove usage. * sysdeps/unix/sysv/linux/powerpc/not-errno.h: Remove file. Reported-by: Breno Leitão <leitao@debian.org> |
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| .. | ||
| bits | ||
| powerpc32 | ||
| powerpc64 | ||
| sys | ||
| configure | ||
| configure.ac | ||
| dl-brk.S | ||
| dl-cache.h | ||
| dl-static.c | ||
| dl-sysdep.c | ||
| elision-conf.c | ||
| elision-conf.h | ||
| elision-lock.c | ||
| elision-timed.c | ||
| elision-trylock.c | ||
| elision-unlock.c | ||
| force-elision.h | ||
| get_clockfreq.c | ||
| get_timebase_freq.c | ||
| getmsg.c | ||
| gettimeofday.c | ||
| htm.h | ||
| Implies | ||
| init-first.c | ||
| ioctl.c | ||
| ipc_priv.h | ||
| kernel_sigaction.h | ||
| kernel_termios.h | ||
| kernel-features.h | ||
| ldconfig.h | ||
| ldd-rewrite.sed | ||
| ldsodefs.h | ||
| libc-start.c | ||
| libc-start.h | ||
| libc-vdso.h | ||
| lowlevellock.h | ||
| Makefile | ||
| nldbl-abi.h | ||
| profil-counter.h | ||
| pt-longjmp.c | ||
| pthread_attr_setstack.c | ||
| pthread_attr_setstacksize.c | ||
| pthread_mutex_cond_lock.c | ||
| pthread_mutex_lock.c | ||
| pthread_mutex_timedlock.c | ||
| pthread_mutex_trylock.c | ||
| putmsg.c | ||
| readelflib.c | ||
| rt-sysdep.c | ||
| sigcontextinfo.h | ||
| syscall.S | ||
| sysconf.c | ||
| sysdep.c | ||
| test-gettimebasefreq.c | ||
| test-powerpc-linux-sysconf.c | ||
| time.c | ||
| Versions | ||