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authorAdhemerval Zanella <adhemerval.zanella@linaro.org>2018-08-27 09:42:50 -0300
committerAdhemerval Zanella <adhemerval.zanella@linaro.org>2018-09-21 10:18:03 -0700
commitf0458cf4f9ff3d870c43b624e6dccaaf657d5e83 (patch)
tree92e48875fbeb81db1890ea1b8f75b5c7ec900ae1 /ChangeLog
parent434d45fd70ac1a137d01b715ea99c03ce3c21b14 (diff)
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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>
Diffstat (limited to 'ChangeLog')
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diff --git a/ChangeLog b/ChangeLog
index 66c58e89268..55214c32764 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -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.
+
2018-09-21 Rafal Luzynski <digitalfreak@lingonborough.com>
[BZ #10425]