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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>
This commit is contained in:
Adhemerval Zanella
parent
434d45fd70
commit
f0458cf4f9
20
ChangeLog
20
ChangeLog
@ -1,3 +1,23 @@
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2018-09-21 Adhemerval Zanella <adhemerval.zanella@linaro.org>
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* NEWS: Add note about new TLE support on powerpc64le.
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* sysdeps/powerpc/nptl/tcb-offsets.sym (TM_CAPABLE): Remove.
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* sysdeps/powerpc/nptl/tls.h (tcbhead_t): Rename tm_capable to
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__ununsed1.
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(TLS_INIT_TP, TLS_DEFINE_INIT_TP): Remove tm_capable setup.
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(THREAD_GET_TM_CAPABLE, THREAD_SET_TM_CAPABLE): Remove macros.
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* sysdeps/powerpc/powerpc32/sysdep.h,
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sysdeps/powerpc/powerpc64/sysdep.h (ABORT_TRANSACTION_IMPL,
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ABORT_TRANSACTION): Remove macros.
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* sysdeps/powerpc/sysdep.h (ABORT_TRANSACTION): Likewise.
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* sysdeps/unix/sysv/linux/powerpc/elision-conf.c (elision_init): Set
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__pthread_force_elision iff PPC_FEATURE2_HTM_NOSC is set.
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* sysdeps/unix/sysv/linux/powerpc/powerpc32/sysdep.h,
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sysdeps/unix/sysv/linux/powerpc/powerpc64/sysdep.h
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sysdeps/unix/sysv/linux/powerpc/syscall.S (ABORT_TRANSACTION): Remove
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usage.
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* sysdeps/unix/sysv/linux/powerpc/not-errno.h: Remove file.
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2018-09-21 Rafal Luzynski <digitalfreak@lingonborough.com>
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[BZ #10425]
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9
NEWS
9
NEWS
@ -21,6 +21,15 @@ Major new features:
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* The reallocarray function is now declared under _DEFAULT_SOURCE, not just
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for _GNU_SOURCE, to match BSD environments.
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* For powercp64le ABI, Transactional Lock Elision is now enabled iff kernel
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indicates that it will abort the transaction prior to entering the kernel
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(PPC_FEATURE2_HTM_NOSC on hwcap2). On older kernels the transaction is
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suspended, and this caused some undefined side-effects issues by aborting
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transactions manually. Glibc avoided it by abort transactions manually on
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each syscall, but it lead to performance issues on newer kernels where the
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HTM state is saved and restore lazily (the state being saved even when the
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process actually does not use HTM).
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Deprecated and removed features, and other changes affecting compatibility:
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* The glibc.tune tunable namespace has been renamed to glibc.cpu and the
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@ -21,7 +21,6 @@ DSO_SLOT2 (offsetof (tcbhead_t, dso_slot2) - TLS_TCB_OFFSET - sizeof (tcbhead_
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#ifdef __powerpc64__
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TCB_AT_PLATFORM (offsetof (tcbhead_t, at_platform) - TLS_TCB_OFFSET - sizeof(tcbhead_t))
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#endif
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TM_CAPABLE (offsetof (tcbhead_t, tm_capable) - TLS_TCB_OFFSET - sizeof (tcbhead_t))
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#ifndef __powerpc64__
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TCB_AT_PLATFORM (offsetof (tcbhead_t, at_platform) - TLS_TCB_OFFSET - sizeof(tcbhead_t))
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PADDING (offsetof (tcbhead_t, padding) - TLS_TCB_OFFSET - sizeof(tcbhead_t))
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@ -67,8 +67,7 @@ typedef struct
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uint32_t padding;
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uint32_t at_platform;
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#endif
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/* Indicate if HTM capable (ISA 2.07). */
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uint32_t tm_capable;
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uint32_t __unused;
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/* Reservation for AT_PLATFORM data - powerpc64. */
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#ifdef __powerpc64__
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uint32_t at_platform;
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@ -142,7 +141,6 @@ register void *__thread_register __asm__ ("r13");
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# define TLS_INIT_TP(tcbp) \
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({ \
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__thread_register = (void *) (tcbp) + TLS_TCB_OFFSET; \
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THREAD_SET_TM_CAPABLE (__tcb_hwcap & PPC_FEATURE2_HAS_HTM ? 1 : 0); \
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THREAD_SET_HWCAP (__tcb_hwcap); \
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THREAD_SET_AT_PLATFORM (__tcb_platform); \
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NULL; \
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@ -151,8 +149,6 @@ register void *__thread_register __asm__ ("r13");
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/* Value passed to 'clone' for initialization of the thread register. */
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# define TLS_DEFINE_INIT_TP(tp, pd) \
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void *tp = (void *) (pd) + TLS_TCB_OFFSET + TLS_PRE_TCB_SIZE; \
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(((tcbhead_t *) ((char *) tp - TLS_TCB_OFFSET))[-1].tm_capable) = \
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THREAD_GET_TM_CAPABLE (); \
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(((tcbhead_t *) ((char *) tp - TLS_TCB_OFFSET))[-1].hwcap) = \
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THREAD_GET_HWCAP (); \
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(((tcbhead_t *) ((char *) tp - TLS_TCB_OFFSET))[-1].at_platform) = \
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@ -210,13 +206,6 @@ register void *__thread_register __asm__ ("r13");
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+ TLS_PRE_TCB_SIZE))[-1].pointer_guard \
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= THREAD_GET_POINTER_GUARD())
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/* tm_capable field in TCB head. */
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# define THREAD_GET_TM_CAPABLE() \
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(((tcbhead_t *) ((char *) __thread_register \
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- TLS_TCB_OFFSET))[-1].tm_capable)
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# define THREAD_SET_TM_CAPABLE(value) \
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(THREAD_GET_TM_CAPABLE () = (value))
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/* hwcap field in TCB head. */
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# define THREAD_GET_HWCAP() \
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(((tcbhead_t *) ((char *) __thread_register \
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@ -90,24 +90,7 @@ GOT_LABEL: ; \
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cfi_endproc; \
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ASM_SIZE_DIRECTIVE(name)
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#if !IS_IN(rtld) && !defined(__SPE__)
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# define ABORT_TRANSACTION_IMPL \
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cmpwi 2,0; \
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beq 1f; \
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lwz 0,TM_CAPABLE(2); \
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cmpwi 0,0; \
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beq 1f; \
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li 11,_ABORT_SYSCALL; \
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tabort. 11; \
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.align 4; \
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1:
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#else
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# define ABORT_TRANSACTION_IMPL
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#endif
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#define ABORT_TRANSACTION ABORT_TRANSACTION_IMPL
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#define DO_CALL(syscall) \
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ABORT_TRANSACTION \
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li 0,syscall; \
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sc
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@ -263,24 +263,7 @@ LT_LABELSUFFIX(name,_name_end): ; \
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TRACEBACK_MASK(name,mask); \
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END_2(name)
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#if !IS_IN(rtld)
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# define ABORT_TRANSACTION_IMPL \
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cmpdi 13,0; \
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beq 1f; \
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lwz 0,TM_CAPABLE(13); \
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cmpwi 0,0; \
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beq 1f; \
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li 11,_ABORT_SYSCALL; \
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tabort. 11; \
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.p2align 4; \
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1:
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#else
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# define ABORT_TRANSACTION_IMPL
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#endif
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#define ABORT_TRANSACTION ABORT_TRANSACTION_IMPL
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#define DO_CALL(syscall) \
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ABORT_TRANSACTION \
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li 0,syscall; \
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sc
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@ -21,8 +21,6 @@
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*/
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#define _SYSDEPS_SYSDEP_H 1
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#include <bits/hwcap.h>
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#include <tls.h>
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#include <htm.h>
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#define PPC_FEATURE_970 (PPC_FEATURE_POWER4 + PPC_FEATURE_HAS_ALTIVEC)
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@ -166,22 +164,4 @@
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#define ALIGNARG(log2) log2
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#define ASM_SIZE_DIRECTIVE(name) .size name,.-name
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#else
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/* Linux kernel powerpc documentation [1] states issuing a syscall inside a
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transaction is not recommended and may lead to undefined behavior. It
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also states syscalls do not abort transactions. To avoid such traps,
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we abort transaction just before syscalls.
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[1] Documentation/powerpc/transactional_memory.txt [Syscalls] */
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#if !IS_IN(rtld) && !defined(__SPE__)
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# define ABORT_TRANSACTION \
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({ \
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if (THREAD_GET_TM_CAPABLE ()) \
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__libc_tabort (_ABORT_SYSCALL); \
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})
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#else
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# define ABORT_TRANSACTION
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#endif
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#endif /* __ASSEMBLER__ */
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@ -127,6 +127,26 @@ elision_init (int argc __attribute__ ((unused)),
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TUNABLE_CALLBACK (set_elision_skip_trylock_internal_abort));
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#endif
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/* Linux from 3.9 through 4.2 do not abort HTM transaction on syscalls,
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instead it suspends the transaction and resumes it when returning to
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usercode. The side-effects of the syscall will always remain visible,
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even if the transaction is aborted. This is an issue when a transaction
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is used along with futex syscall, on pthread_cond_wait for instance,
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where futex might succeed but the transaction is rolled back leading
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the condition variable object in an inconsistent state.
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Glibc used to prevent it by always aborting a transaction before issuing
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a syscall. Linux 4.2 also decided to abort active transaction in
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syscalls which makes the glibc workaround superflours. Worse, glibc
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transaction abortions leads to a performance issues on recent kernels.
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So Lock Elision is just enabled when it has been explict set (either
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by tunables of by a configure switch) and if kernel aborts HTM
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transactions on syscalls (PPC_FEATURE2_HTM_NOSC) */
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__pthread_force_elision = (__pthread_force_elision
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&& GLRO (dl_hwcap2) & PPC_FEATURE2_HTM_NOSC);
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if (!__pthread_force_elision)
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__elision_aconf.try_tbegin = 0; /* Disable elision on rwlocks. */
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}
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@ -1,30 +0,0 @@
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/* Syscall wrapper that do not set errno. Linux powerpc version.
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Copyright (C) 2018 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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/* __access_noerrno is used during process initialization in elf/dl-tunables.c
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before the TCB is initialized, prohibiting the usage of
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ABORT_TRANSACTION. */
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#undef ABORT_TRANSACTION
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#define ABORT_TRANSACTION
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#include "sysdeps/unix/sysv/linux/not-errno.h"
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/* Recover ABORT_TRANSACTION's previous value, in order to not affect
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other syscalls. */
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#undef ABORT_TRANSACTION
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#define ABORT_TRANSACTION ABORT_TRANSACTION_IMPL
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@ -109,7 +109,6 @@
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register long int r11 __asm__ ("r11"); \
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register long int r12 __asm__ ("r12"); \
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LOADARGS_##nr(name, args); \
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ABORT_TRANSACTION; \
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__asm__ __volatile__ \
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("sc \n\t" \
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"mfcr %0" \
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@ -131,7 +131,6 @@
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register long int r7 __asm__ ("r7"); \
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register long int r8 __asm__ ("r8"); \
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LOADARGS_##nr (name, ##args); \
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ABORT_TRANSACTION; \
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__asm__ __volatile__ \
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("sc\n\t" \
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"mfcr %0\n\t" \
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@ -18,7 +18,6 @@
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#include <sysdep.h>
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ENTRY (syscall)
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ABORT_TRANSACTION
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mr r0,r3
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mr r3,r4
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mr r4,r5
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