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>

5 files changed, 1 insertions, 67 deletions

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 <bits/hwcap.h>
-#include <tls.h>
-#include <htm.h>
 
 #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__ */