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)
+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]
\f
Version 2.28.1
+Deprecated and removed features, and other changes affecting compatibility:
+
+* For powercp64le ABI, Transactional Lock Elision is now enabled iff kernel
+ indicates that it will abort the transaction prior to entering the kernel
+ (PPC_FEATURE2_HTM_NOSC on hwcap2). On older kernels the transaction is
+ suspended, and this caused some undefined side-effects issues by aborting
+ transactions manually. Glibc avoided it by abort transactions manually on
+ each syscall, but it lead to performance issues on newer kernels where the
+ HTM state is saved and restore lazily (the state being saved even when the
+ process actually does not use HTM).
+
The following bugs are resolved with this release:
[19444] build failures with -O1 due to -Wmaybe-uninitialized
#ifdef __powerpc64__
TCB_AT_PLATFORM (offsetof (tcbhead_t, at_platform) - TLS_TCB_OFFSET - sizeof(tcbhead_t))
#endif
-TM_CAPABLE (offsetof (tcbhead_t, tm_capable) - TLS_TCB_OFFSET - sizeof (tcbhead_t))
#ifndef __powerpc64__
TCB_AT_PLATFORM (offsetof (tcbhead_t, at_platform) - TLS_TCB_OFFSET - sizeof(tcbhead_t))
PADDING (offsetof (tcbhead_t, padding) - TLS_TCB_OFFSET - sizeof(tcbhead_t))
uint32_t padding;
uint32_t at_platform;
#endif
- /* Indicate if HTM capable (ISA 2.07). */
- uint32_t tm_capable;
+ uint32_t __unused;
/* Reservation for AT_PLATFORM data - powerpc64. */
#ifdef __powerpc64__
uint32_t at_platform;
# define TLS_INIT_TP(tcbp) \
({ \
__thread_register = (void *) (tcbp) + TLS_TCB_OFFSET; \
- THREAD_SET_TM_CAPABLE (__tcb_hwcap & PPC_FEATURE2_HAS_HTM ? 1 : 0); \
THREAD_SET_HWCAP (__tcb_hwcap); \
THREAD_SET_AT_PLATFORM (__tcb_platform); \
NULL; \
/* Value passed to 'clone' for initialization of the thread register. */
# define TLS_DEFINE_INIT_TP(tp, pd) \
void *tp = (void *) (pd) + TLS_TCB_OFFSET + TLS_PRE_TCB_SIZE; \
- (((tcbhead_t *) ((char *) tp - TLS_TCB_OFFSET))[-1].tm_capable) = \
- THREAD_GET_TM_CAPABLE (); \
(((tcbhead_t *) ((char *) tp - TLS_TCB_OFFSET))[-1].hwcap) = \
THREAD_GET_HWCAP (); \
(((tcbhead_t *) ((char *) tp - TLS_TCB_OFFSET))[-1].at_platform) = \
+ TLS_PRE_TCB_SIZE))[-1].pointer_guard \
= THREAD_GET_POINTER_GUARD())
-/* tm_capable field in TCB head. */
-# define THREAD_GET_TM_CAPABLE() \
- (((tcbhead_t *) ((char *) __thread_register \
- - TLS_TCB_OFFSET))[-1].tm_capable)
-# define THREAD_SET_TM_CAPABLE(value) \
- (THREAD_GET_TM_CAPABLE () = (value))
-
/* hwcap field in TCB head. */
# define THREAD_GET_HWCAP() \
(((tcbhead_t *) ((char *) __thread_register \
cfi_endproc; \
ASM_SIZE_DIRECTIVE(name)
-#if !IS_IN(rtld) && !defined(__SPE__)
-# define ABORT_TRANSACTION_IMPL \
- cmpwi 2,0; \
- beq 1f; \
- lwz 0,TM_CAPABLE(2); \
- cmpwi 0,0; \
- beq 1f; \
- li 11,_ABORT_SYSCALL; \
- tabort. 11; \
- .align 4; \
-1:
-#else
-# define ABORT_TRANSACTION_IMPL
-#endif
-#define ABORT_TRANSACTION ABORT_TRANSACTION_IMPL
-
#define DO_CALL(syscall) \
- ABORT_TRANSACTION \
li 0,syscall; \
sc
TRACEBACK_MASK(name,mask); \
END_2(name)
-#if !IS_IN(rtld)
-# define ABORT_TRANSACTION_IMPL \
- cmpdi 13,0; \
- beq 1f; \
- lwz 0,TM_CAPABLE(13); \
- cmpwi 0,0; \
- beq 1f; \
- li 11,_ABORT_SYSCALL; \
- tabort. 11; \
- .p2align 4; \
-1:
-#else
-# define ABORT_TRANSACTION_IMPL
-#endif
-#define ABORT_TRANSACTION ABORT_TRANSACTION_IMPL
-
#define DO_CALL(syscall) \
- ABORT_TRANSACTION \
li 0,syscall; \
sc
*/
#define _SYSDEPS_SYSDEP_H 1
#include <bits/hwcap.h>
-#include <tls.h>
-#include <htm.h>
#define PPC_FEATURE_970 (PPC_FEATURE_POWER4 + PPC_FEATURE_HAS_ALTIVEC)
#define ALIGNARG(log2) log2
#define ASM_SIZE_DIRECTIVE(name) .size name,.-name
-#else
-
-/* Linux kernel powerpc documentation [1] states issuing a syscall inside a
- transaction is not recommended and may lead to undefined behavior. It
- also states syscalls do not abort transactions. To avoid such traps,
- we abort transaction just before syscalls.
-
- [1] Documentation/powerpc/transactional_memory.txt [Syscalls] */
-#if !IS_IN(rtld) && !defined(__SPE__)
-# define ABORT_TRANSACTION \
- ({ \
- if (THREAD_GET_TM_CAPABLE ()) \
- __libc_tabort (_ABORT_SYSCALL); \
- })
-#else
-# define ABORT_TRANSACTION
-#endif
-
#endif /* __ASSEMBLER__ */
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. */
}
+++ /dev/null
-/* 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
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" \
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" \
#include <sysdep.h>
ENTRY (syscall)
- ABORT_TRANSACTION
mr r0,r3
mr r3,r4
mr r4,r5
projects / thirdparty / glibc.git / commitdiff
