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>
29 lines
1.1 KiB
Plaintext
29 lines
1.1 KiB
Plaintext
#include <sysdep.h>
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#include <tls.h>
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#include <kernel-features.h>
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--
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-- Abuse tls.h macros to derive offsets relative to the thread register.
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# undef __thread_register
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# define __thread_register ((void *) 0)
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# define thread_offsetof(mem) ((ptrdiff_t) THREAD_SELF + offsetof (struct pthread, mem))
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#if TLS_MULTIPLE_THREADS_IN_TCB
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MULTIPLE_THREADS_OFFSET thread_offsetof (header.multiple_threads)
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#endif
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TID thread_offsetof (tid)
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POINTER_GUARD (offsetof (tcbhead_t, pointer_guard) - TLS_TCB_OFFSET - sizeof (tcbhead_t))
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TAR_SAVE (offsetof (tcbhead_t, tar_save) - TLS_TCB_OFFSET - sizeof (tcbhead_t))
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DSO_SLOT1 (offsetof (tcbhead_t, dso_slot1) - TLS_TCB_OFFSET - sizeof (tcbhead_t))
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DSO_SLOT2 (offsetof (tcbhead_t, dso_slot2) - TLS_TCB_OFFSET - sizeof (tcbhead_t))
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#ifdef __powerpc64__
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TCB_AT_PLATFORM (offsetof (tcbhead_t, at_platform) - TLS_TCB_OFFSET - sizeof(tcbhead_t))
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#endif
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#ifndef __powerpc64__
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TCB_AT_PLATFORM (offsetof (tcbhead_t, at_platform) - TLS_TCB_OFFSET - sizeof(tcbhead_t))
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PADDING (offsetof (tcbhead_t, padding) - TLS_TCB_OFFSET - sizeof(tcbhead_t))
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#endif
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TCB_HWCAP (offsetof (tcbhead_t, hwcap) - TLS_TCB_OFFSET - sizeof (tcbhead_t))
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