gscope + private_futex for alpha

gscope + private_futex for alpha

[Richard Henderson]

It seems like much of this same code could be shared with all
of the targets, particularly those that define TLS_DTV_AT_TP.


r~


2007-05-24  Richard Henderson  <rth@redhat.com>

	* descr.h (struct pthread): Add header.gscope_flag and
	header.private_futex.
	* nptl/sysdeps/alpha/tls.h (THREAD_GSCOPE_FLAG_UNUSED): New.
	(THREAD_GSCOPE_FLAG_USED, THREAD_GSCOPE_FLAG_WAIT): New.
	(THREAD_GSCOPE_RESET_FLAG, THREAD_GSCOPE_SET_FLAG): New.
	(THREAD_GSCOPE_WAIT): New.
	* nptl/sysdeps/unix/sysv/linux/alpha/lowlevellock.h
	(FUTEX_PRIVATE_FLAG): New.
	(lll_futex_wait_flags): New.
	* nptl/sysdeps/unix/sysv/linux/alpha/pthread_once.c (__pthread_once):
	Pass FUTEX_PRIVATE_FLAG or header.private_futex down to the
	futex call.

Index: nptl/descr.h
===================================================================
RCS file: /cvs/glibc/libc/nptl/descr.h,v
retrieving revision 1.39
diff -u -p -d -r1.39 descr.h
--- nptl/descr.h	11 May 2007 06:11:48 -0000	1.39
+++ nptl/descr.h	24 May 2007 23:49:08 -0000
@@ -131,6 +131,8 @@ struct pthread
     struct
     {
       int multiple_threads;
+      int gscope_flag;
+      int private_futex;
     } header;
 #endif
 
Index: nptl/sysdeps/alpha/tls.h
===================================================================
RCS file: /cvs/glibc/libc/nptl/sysdeps/alpha/tls.h,v
retrieving revision 1.7
diff -u -p -d -r1.7 tls.h
--- nptl/sysdeps/alpha/tls.h	27 Oct 2006 23:11:43 -0000	1.7
+++ nptl/sysdeps/alpha/tls.h	24 May 2007 23:49:08 -0000
@@ -121,6 +121,36 @@ typedef struct
 #define THREAD_SETMEM_NC(descr, member, idx, value) \
   descr->member[idx] = (value)
 
+/* Get and set the global scope generation counter in the TCB head.  */
+#define THREAD_GSCOPE_FLAG_UNUSED 0
+#define THREAD_GSCOPE_FLAG_USED   1
+#define THREAD_GSCOPE_FLAG_WAIT   2
+
+#define THREAD_GSCOPE_RESET_FLAG()					\
+  do {									\
+    int __res = atomic_exchange_rel(&THREAD_SELF->header.gscope_flag,	\
+				    THREAD_GSCOPE_FLAG_UNUSED);		\
+    if (__res == THREAD_GSCOPE_FLAG_WAIT)				\
+      lll_futex_wake (&THREAD_SELF->header.gscope_flag, 1);		\
+  } while (0)
+
+#define THREAD_GSCOPE_SET_FLAG()					\
+  do {									\
+    THREAD_SELF->header.gscope_flag = THREAD_GSCOPE_FLAG_USED;		\
+    __sync_synchronize ();						\
+  } while (0)
+
+#ifdef PTR_DEMANGLE
+# define THREAD_GSCOPE_WAIT()						\
+  do {									\
+    void (*ptr)(void) = GL(dl_wait_lookup_done);			\
+    PTR_DEMANGLE (ptr);							\
+    ptr ();								\
+  } while (0)
+#else
+# define THREAD_GSCOPE_WAIT()  GL(dl_wait_lookup_done) ()
+#endif
+ 
 #endif /* __ASSEMBLER__ */
 
 #endif	/* tls.h */
Index: nptl/sysdeps/unix/sysv/linux/alpha/lowlevellock.h
===================================================================
RCS file: /cvs/glibc/libc/nptl/sysdeps/unix/sysv/linux/alpha/lowlevellock.h,v
retrieving revision 1.8
diff -u -p -d -r1.8 lowlevellock.h
--- nptl/sysdeps/unix/sysv/linux/alpha/lowlevellock.h	29 Jul 2006 05:06:07 -0000	1.8
+++ nptl/sysdeps/unix/sysv/linux/alpha/lowlevellock.h	24 May 2007 23:49:08 -0000
@@ -36,6 +36,7 @@
 #define FUTEX_LOCK_PI		6
 #define FUTEX_UNLOCK_PI		7
 #define FUTEX_TRYLOCK_PI	8
+#define FUTEX_PRIVATE_FLAG      128
 
 /* Initializer for compatibility lock.	*/
 #define LLL_MUTEX_LOCK_INITIALIZER (0)
@@ -49,6 +50,15 @@
     INTERNAL_SYSCALL_ERROR_P (__ret, __err)? -__ret : __ret;		      \
   })
 
+#define lll_futex_wait_flags(futexp, val, flags) \
+  ({									      \
+    INTERNAL_SYSCALL_DECL (__err);					      \
+    long int __ret;							      \
+    __ret = INTERNAL_SYSCALL (futex, __err, 4,				      \
+			      (futexp), FUTEX_WAIT | (flags), (val), 0);      \
+    INTERNAL_SYSCALL_ERROR_P (__ret, __err)? -__ret : __ret;		      \
+  })
+
 #define lll_futex_timed_wait(futexp, val, timespec) \
   ({									      \
     INTERNAL_SYSCALL_DECL (__err);					      \
Index: nptl/sysdeps/unix/sysv/linux/alpha/pthread_once.c
===================================================================
RCS file: /cvs/glibc/libc/nptl/sysdeps/unix/sysv/linux/alpha/pthread_once.c,v
retrieving revision 1.2
diff -u -p -d -r1.2 pthread_once.c
--- nptl/sysdeps/unix/sysv/linux/alpha/pthread_once.c	8 Sep 2004 06:11:35 -0000	1.2
+++ nptl/sysdeps/unix/sysv/linux/alpha/pthread_once.c	24 May 2007 23:49:08 -0000
@@ -34,6 +34,12 @@ clear_once_control (void *arg)
 int
 __pthread_once (pthread_once_t *once_control, void (*init_routine) (void))
 {
+#ifdef __ASSUME_PRIVATE_FUTEX
+  const int futex_private_flag = FUTEX_PRIVATE_FLAG;
+#else
+  const int futex_private_flag = THREAD_SELF->header.private_futex;
+#endif
+
   for (;;)
     {
       int oldval;
@@ -72,7 +78,7 @@ __pthread_once (pthread_once_t *once_con
 	break;
 
       /* Same generation, some other thread was faster. Wait.  */
-      lll_futex_wait (once_control, oldval);
+      lll_futex_wait_flags (once_control, oldval, futex_private_flag);
     }
 
   /* This thread is the first here.  Do the initialization.

Re: gscope + private_futex for alpha

[Ulrich Drepper]

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Richard Henderson wrote:
> It seems like much of this same code could be shared with all
> of the targets, particularly those that define TLS_DTV_AT_TP.

Jakub has some patches which I haven't yet looked at.


> +#define lll_futex_wait_flags(futexp, val, flags) \

I don't think this is what I want to do.  The reason is obvious from the
rest of your changes.  Your pthread_once cannot work since the wake call
doesn't use the private flag the same way.  If we'd introduce a new
macro like that we'd have a whole lot of places to inspect and debug.

I'm looking at the generic situation right soon since even x86-64 needs
it for mutexes etc.  What I'll probably end up doing it extend the
existing macros.  This way every usage has to be inspected.

- --
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖
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Re: gscope + private_futex for alpha

[Richard Henderson]

On Thu, May 24, 2007 at 07:25:53PM -0700, Ulrich Drepper wrote:
> > It seems like much of this same code could be shared with all
> > of the targets, particularly those that define TLS_DTV_AT_TP.
> 
> Jakub has some patches which I haven't yet looked at.

Yeah, Jakub puts the flag in a ppc specific place.  I thought it
used the same scheme as ia64 and alpha though, and it would seem
the common header would be ideal.

> I don't think this is what I want to do.  The reason is obvious from the
> rest of your changes.  Your pthread_once cannot work since the wake call
> doesn't use the private flag the same way.

Ah, I didn't realize this was a requirement.  I've not yet
managed to boot a new kernel with this support present.


r~

Re: gscope + private_futex for alpha

[Ulrich Drepper]

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Richard Henderson wrote:
> Yeah, Jakub puts the flag in a ppc specific place.  I thought it
> used the same scheme as ia64 and alpha though, and it would seem
> the common header would be ideal.

It's really a toss up.  Jakub mentioned that he thought your approach is
good.  We'll see whether it's better in his opinion to warrant him
writing another patch.

- --
➧ Ulrich Drepper ➧ Red Hat, Inc. ➧ 444 Castro St ➧ Mountain View, CA ❖
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