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author | Adhemerval Zanella <adhemerval.zanella@linaro.org> | 2018-08-27 09:42:50 -0300 |
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committer | Adhemerval Zanella <adhemerval.zanella@linaro.org> | 2018-09-21 10:18:03 -0700 |
commit | f0458cf4f9ff3d870c43b624e6dccaaf657d5e83 (patch) | |
tree | 92e48875fbeb81db1890ea1b8f75b5c7ec900ae1 /sysdeps/unix/sysv/linux/powerpc | |
parent | 434d45fd70ac1a137d01b715ea99c03ce3c21b14 (diff) | |
download | glibc-f0458cf4f9ff3d870c43b624e6dccaaf657d5e83.tar.gz glibc-f0458cf4f9ff3d870c43b624e6dccaaf657d5e83.tar.xz glibc-f0458cf4f9ff3d870c43b624e6dccaaf657d5e83.zip |
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 'sysdeps/unix/sysv/linux/powerpc')
-rw-r--r-- | sysdeps/unix/sysv/linux/powerpc/elision-conf.c | 20 | ||||
-rw-r--r-- | sysdeps/unix/sysv/linux/powerpc/not-errno.h | 30 | ||||
-rw-r--r-- | sysdeps/unix/sysv/linux/powerpc/powerpc32/sysdep.h | 1 | ||||
-rw-r--r-- | sysdeps/unix/sysv/linux/powerpc/powerpc64/sysdep.h | 1 | ||||
-rw-r--r-- | sysdeps/unix/sysv/linux/powerpc/syscall.S | 1 |
5 files changed, 20 insertions, 33 deletions
diff --git a/sysdeps/unix/sysv/linux/powerpc/elision-conf.c b/sysdeps/unix/sysv/linux/powerpc/elision-conf.c index 906882a65e..fc82bd1ad8 100644 --- a/sysdeps/unix/sysv/linux/powerpc/elision-conf.c +++ b/sysdeps/unix/sysv/linux/powerpc/elision-conf.c @@ -127,6 +127,26 @@ elision_init (int argc __attribute__ ((unused)), TUNABLE_CALLBACK (set_elision_skip_trylock_internal_abort)); #endif + /* Linux from 3.9 through 4.2 do not abort HTM transaction on syscalls, + instead it suspends the transaction and resumes it when returning to + usercode. The side-effects of the syscall will always remain visible, + even if the transaction is aborted. This is an issue when a transaction + is used along with futex syscall, on pthread_cond_wait for instance, + where futex might succeed but the transaction is rolled back leading + the condition variable 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 superflours. Worse, glibc + transaction abortions leads to a performance issues on recent kernels. + + So Lock Elision is just enabled when it has been explict set (either + by tunables of by a configure switch) and if kernel aborts HTM + transactions on syscalls (PPC_FEATURE2_HTM_NOSC) */ + + __pthread_force_elision = (__pthread_force_elision + && GLRO (dl_hwcap2) & PPC_FEATURE2_HTM_NOSC); + if (!__pthread_force_elision) __elision_aconf.try_tbegin = 0; /* Disable elision on rwlocks. */ } diff --git a/sysdeps/unix/sysv/linux/powerpc/not-errno.h b/sysdeps/unix/sysv/linux/powerpc/not-errno.h deleted file mode 100644 index 27da21bdf1..0000000000 --- a/sysdeps/unix/sysv/linux/powerpc/not-errno.h +++ /dev/null @@ -1,30 +0,0 @@ -/* Syscall wrapper that do not set errno. Linux powerpc version. - Copyright (C) 2018 Free Software Foundation, Inc. - This file is part of the GNU C Library. - - The GNU C Library is free software; you can redistribute it and/or - modify it under the terms of the GNU Lesser General Public - License as published by the Free Software Foundation; either - version 2.1 of the License, or (at your option) any later version. - - The GNU C Library is distributed in the hope that it will be useful, - but WITHOUT ANY WARRANTY; without even the implied warranty of - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU - Lesser General Public License for more details. - - You should have received a copy of the GNU Lesser General Public - License along with the GNU C Library; if not, see - <http://www.gnu.org/licenses/>. */ - -/* __access_noerrno is used during process initialization in elf/dl-tunables.c - before the TCB is initialized, prohibiting the usage of - ABORT_TRANSACTION. */ -#undef ABORT_TRANSACTION -#define ABORT_TRANSACTION - -#include "sysdeps/unix/sysv/linux/not-errno.h" - -/* Recover ABORT_TRANSACTION's previous value, in order to not affect - other syscalls. */ -#undef ABORT_TRANSACTION -#define ABORT_TRANSACTION ABORT_TRANSACTION_IMPL diff --git a/sysdeps/unix/sysv/linux/powerpc/powerpc32/sysdep.h b/sysdeps/unix/sysv/linux/powerpc/powerpc32/sysdep.h index f7277d59e1..ec5c5250f8 100644 --- a/sysdeps/unix/sysv/linux/powerpc/powerpc32/sysdep.h +++ b/sysdeps/unix/sysv/linux/powerpc/powerpc32/sysdep.h @@ -109,7 +109,6 @@ register long int r11 __asm__ ("r11"); \ register long int r12 __asm__ ("r12"); \ LOADARGS_##nr(name, args); \ - ABORT_TRANSACTION; \ __asm__ __volatile__ \ ("sc \n\t" \ "mfcr %0" \ diff --git a/sysdeps/unix/sysv/linux/powerpc/powerpc64/sysdep.h b/sysdeps/unix/sysv/linux/powerpc/powerpc64/sysdep.h index 0956cf04a7..1f17f7bd5f 100644 --- a/sysdeps/unix/sysv/linux/powerpc/powerpc64/sysdep.h +++ b/sysdeps/unix/sysv/linux/powerpc/powerpc64/sysdep.h @@ -131,7 +131,6 @@ register long int r7 __asm__ ("r7"); \ register long int r8 __asm__ ("r8"); \ LOADARGS_##nr (name, ##args); \ - ABORT_TRANSACTION; \ __asm__ __volatile__ \ ("sc\n\t" \ "mfcr %0\n\t" \ diff --git a/sysdeps/unix/sysv/linux/powerpc/syscall.S b/sysdeps/unix/sysv/linux/powerpc/syscall.S index 2da91721be..bbab613aca 100644 --- a/sysdeps/unix/sysv/linux/powerpc/syscall.S +++ b/sysdeps/unix/sysv/linux/powerpc/syscall.S @@ -18,7 +18,6 @@ #include <sysdep.h> ENTRY (syscall) - ABORT_TRANSACTION mr r0,r3 mr r3,r4 mr r4,r5 |