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| author | Adhemerval Zanella <adhemerval.zanella@linaro.org> | 2018-08-27 09:42:50 -0300 |
|---|---|---|
| committer | Florian Weimer <fweimer@redhat.com> | 2019-02-27 17:36:47 +0100 |
| commit | e5366c12d0453ab754ab5dc2d1e7b98966b0988c (patch) | |
| tree | 614b27987a49eda071dfb9336f502e80d903c74a /ChangeLog | |
| parent | 384113d1c0ec1b89c38c6e4c1967f827d7f6f1c8 (diff) | |
| download | glibc-e5366c12d0453ab754ab5dc2d1e7b98966b0988c.tar.gz | |
powerpc: Only enable TLE with PPC_FEATURE2_HTM_NOSC
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>
(cherry picked from commit f0458cf4f9ff3d870c43b624e6dccaaf657d5e83)
Diffstat (limited to 'ChangeLog')
| -rw-r--r-- | ChangeLog | 20 |
1 files changed, 20 insertions, 0 deletions
@@ -1,3 +1,23 @@ +2018-09-21 Adhemerval Zanella <adhemerval.zanella@linaro.org> + + * 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. + 2019-01-13 Jim Wilson <jimw@sifive.com> [BZ #24040] |