S/390: Port of lock elision to System/z

Added support for TX lock elision of pthread mutexes on s390 and
s390x.  This may improve lock scaling of existing programs on TX
capable systems.  The lock elision code is only built with
--enable-lock-elision=yes and then requires a GCC version supporting
the TX builtins.  With lock elision default mutexes are elided via
__builtin_tbegin, if the cpu supports transactions. By default lock
elision is not enabled and the elision code is not built.

1 files changed, 119 insertions, 0 deletions

diff --git a/nptl/sysdeps/unix/sysv/linux/s390/elision-lock.c b/nptl/sysdeps/unix/sysv/linux/s390/elision-lock.c
new file mode 100644
index 0000000000..ba5338fbb9
--- /dev/null
+++ b/nptl/sysdeps/unix/sysv/linux/s390/elision-lock.c
@@ -0,0 +1,119 @@
+/* Elided pthread mutex lock.
+   Copyright (C) 2014 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/>.  */
+
+#include <pthread.h>
+#include <pthreadP.h>
+#include <lowlevellock.h>
+#include <htmintrin.h>
+#include <elision-conf.h>
+#include <stdint.h>
+
+#if !defined(LLL_LOCK) && !defined(EXTRAARG)
+/* Make sure the configuration code is always linked in for static
+   libraries.  */
+#include "elision-conf.c"
+#endif
+
+#ifndef EXTRAARG
+#define EXTRAARG
+#endif
+#ifndef LLL_LOCK
+#define LLL_LOCK(a,b) lll_lock(a,b), 0
+#endif
+
+#define aconf __elision_aconf
+
+/* Adaptive lock using transactions.
+   By default the lock region is run as a transaction, and when it
+   aborts or the lock is busy the lock adapts itself.  */
+
+int
+__lll_lock_elision (int *futex, short *adapt_count, EXTRAARG int private)
+{
+  if (*adapt_count > 0)
+    {
+      /* Lost updates are possible, but harmless.  Due to races this might lead
+	 to *adapt_count becoming less than zero.  */
+      (*adapt_count)--;
+      goto use_lock;
+    }
+
+  __asm__ volatile (".machinemode \"zarch_nohighgprs\"\n\t"
+		    ".machine \"all\""
+		    : : : "memory");
+
+  int try_tbegin;
+  for (try_tbegin = aconf.try_tbegin;
+       try_tbegin > 0;
+       try_tbegin--)
+    {
+      unsigned status;
+      if (__builtin_expect
+	  ((status = __builtin_tbegin((void *)0)) == _HTM_TBEGIN_STARTED, 1))
+	{
+	  if (*futex == 0)
+	    return 0;
+	  /* Lock was busy.  Fall back to normal locking.  */
+	  if (__builtin_expect (__builtin_tx_nesting_depth (), 1))
+	    {
+	      /* In a non-nested transaction there is no need to abort,
+		 which is expensive.  */
+	      __builtin_tend ();
+	      if (aconf.skip_lock_busy > 0)
+		*adapt_count = aconf.skip_lock_busy;
+	      goto use_lock;
+	    }
+	  else /* nesting depth is > 1 */
+	    {
+	      /* A nested transaction will abort eventually because it
+		 cannot make any progress before *futex changes back to 0.
+		 So we may as well abort immediately.
+		 This persistently aborts the outer transaction to force
+		 the outer mutex use the default lock instead of retrying
+		 with transactions until the try_tbegin of the outer mutex
+		 is zero.
+		 The adapt_count of this inner mutex is not changed,
+		 because using the default lock with the inner mutex
+		 would abort the outer transaction.
+	      */
+	      __builtin_tabort (_HTM_FIRST_USER_ABORT_CODE | 1);
+	    }
+	}
+      else
+	{
+	  if (status != _HTM_TBEGIN_TRANSIENT)
+	    {
+	      /* A persistent abort (cc 1 or 3) indicates that a retry is
+		 probably futile.  Use the normal locking now and for the
+		 next couple of calls.
+		 Be careful to avoid writing to the lock.  */
+	      if (aconf.skip_lock_internal_abort > 0)
+		*adapt_count = aconf.skip_lock_internal_abort;
+	      goto use_lock;
+	    }
+	}
+    }
+
+  /* Same logic as above, but for for a number of temporary failures in a
+     row.  */
+  if (aconf.skip_lock_out_of_tbegin_retries > 0 && aconf.try_tbegin > 0)
+    *adapt_count = aconf.skip_lock_out_of_tbegin_retries;
+
+  use_lock:
+  return LLL_LOCK ((*futex), private);
+}