commit f0458cf4f9ff3d870c43b624e6dccaaf657d5e83 Author: Adhemerval Zanella Date: Mon Aug 27 09:42:50 2018 -0300 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 diff --git a/sysdeps/powerpc/nptl/tcb-offsets.sym b/sysdeps/powerpc/nptl/tcb-offsets.sym index e5bb2b3..4c01615 100644 --- a/sysdeps/powerpc/nptl/tcb-offsets.sym +++ b/sysdeps/powerpc/nptl/tcb-offsets.sym @@ -21,7 +21,6 @@ DSO_SLOT2 (offsetof (tcbhead_t, dso_slot2) - TLS_TCB_OFFSET - sizeof (tcbhead_ #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)) diff --git a/sysdeps/powerpc/nptl/tls.h b/sysdeps/powerpc/nptl/tls.h index f88fed5..8317ca7 100644 --- a/sysdeps/powerpc/nptl/tls.h +++ b/sysdeps/powerpc/nptl/tls.h @@ -67,8 +67,7 @@ typedef struct 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; @@ -142,7 +141,6 @@ register void *__thread_register __asm__ ("r13"); # 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; \ @@ -151,8 +149,6 @@ register void *__thread_register __asm__ ("r13"); /* 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) = \ @@ -210,13 +206,6 @@ register void *__thread_register __asm__ ("r13"); + 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 \ diff --git a/sysdeps/powerpc/powerpc32/sysdep.h b/sysdeps/powerpc/powerpc32/sysdep.h index 5f1294e..93097c5 100644 --- a/sysdeps/powerpc/powerpc32/sysdep.h +++ b/sysdeps/powerpc/powerpc32/sysdep.h @@ -90,24 +90,7 @@ GOT_LABEL: ; \ 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 diff --git a/sysdeps/powerpc/powerpc64/sysdep.h b/sysdeps/powerpc/powerpc64/sysdep.h index 2df1d9b..50e64f9 100644 --- a/sysdeps/powerpc/powerpc64/sysdep.h +++ b/sysdeps/powerpc/powerpc64/sysdep.h @@ -263,24 +263,7 @@ LT_LABELSUFFIX(name,_name_end): ; \ 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 diff --git a/sysdeps/powerpc/sysdep.h b/sysdeps/powerpc/sysdep.h index 8a6d236..c8bf25e 100644 --- a/sysdeps/powerpc/sysdep.h +++ b/sysdeps/powerpc/sysdep.h @@ -21,8 +21,6 @@ */ #define _SYSDEPS_SYSDEP_H 1 #include -#include -#include #define PPC_FEATURE_970 (PPC_FEATURE_POWER4 + PPC_FEATURE_HAS_ALTIVEC) @@ -166,22 +164,4 @@ #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__ */ diff --git a/sysdeps/unix/sysv/linux/powerpc/elision-conf.c b/sysdeps/unix/sysv/linux/powerpc/elision-conf.c index 906882a..fc82bd1 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 27da21b..0000000 --- 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 - . */ - -/* __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 f7277d5..ec5c525 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 0956cf0..1f17f7b 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 2da9172..bbab613 100644 --- a/sysdeps/unix/sysv/linux/powerpc/syscall.S +++ b/sysdeps/unix/sysv/linux/powerpc/syscall.S @@ -18,7 +18,6 @@ #include ENTRY (syscall) - ABORT_TRANSACTION mr r0,r3 mr r3,r4 mr r4,r5