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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 | ||
| fpu | ||
| nofpu | ||
| nptl | ||
| power4 | ||
| power5+/fpu | ||
| power6 | ||
| power7/fpu | ||
| powerpc32 | ||
| powerpc64 | ||
| sys/platform | ||
| abort-instr.h | ||
| atomic-machine.h | ||
| cpu-features.c | ||
| cpu-features.h | ||
| dl-procinfo.c | ||
| dl-procinfo.h | ||
| dl-tls.c | ||
| dl-tls.h | ||
| dl-tunables.list | ||
| ffs.c | ||
| fpu_control.h | ||
| gccframe.h | ||
| hwcapinfo.c | ||
| hwcapinfo.h | ||
| ifunc-sel.h | ||
| jmpbuf-offsets.h | ||
| jmpbuf-unwind.h | ||
| ldsodefs.h | ||
| libc-tls.c | ||
| locale-defines.sym | ||
| longjmp.c | ||
| machine-gmon.h | ||
| Makefile | ||
| math-tests-snan-cast.h | ||
| memusage.h | ||
| mod-tlsopt-powerpc.c | ||
| mp_clz_tab.c | ||
| novmx-longjmp.c | ||
| novmx-sigjmp.c | ||
| novmxsetjmp.h | ||
| preconfigure | ||
| rtld-global-offsets.sym | ||
| sched_cpucount.c | ||
| sigjmp.c | ||
| sotruss-lib.c | ||
| stackinfo.h | ||
| sysdep.h | ||
| test-arith.c | ||
| test-arithf.c | ||
| test-get_hwcap-static.c | ||
| test-get_hwcap.c | ||
| test-gettimebase.c | ||
| tls-macros.h | ||
| tst-set_ppr.c | ||
| tst-stack-align.h | ||
| tst-tlsifunc-static.c | ||
| tst-tlsifunc.c | ||
| tst-tlsopt-powerpc.c | ||
| Versions | ||