[PATCH] nptl: Eliminate <smp.h> and __is_smp

[Adhemerval Zanella]

On 13/11/2020 06:45, Florian Weimer via Libc-alpha wrote:
> Most systems are SMP, so optimizing for the UP case is no longer
> approriate.  A dynamic check based on the kernel identification
> has been only implemented for i386 anyway.
> 
> To disable adaptive mutexes on sh, define DEFAULT_ADAPTIVE_COUNT
> as zero for this architecture.

LGTM, thanks.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> 
> ---
>  nptl/nptl-init.c                                 |  4 --
>  nptl/pthreadP.h                                  |  3 --
>  nptl/pthread_mutex_lock.c                        |  3 --
>  nptl/pthread_mutex_timedlock.c                   |  3 --
>  nptl/smp.h                                       | 27 ------------
>  nptl/vars.c                                      |  3 --
>  sysdeps/unix/sysv/linux/i386/smp.h               | 55 ------------------------
>  sysdeps/unix/sysv/linux/sh/adaptive_spin_count.h | 20 +++++++++
>  sysdeps/unix/sysv/linux/sh/smp.h                 | 23 ----------
>  9 files changed, 20 insertions(+), 121 deletions(-)
> 
> diff --git a/nptl/nptl-init.c b/nptl/nptl-init.c
> index 95c60a524a..4aa1231bec 100644
> --- a/nptl/nptl-init.c
> +++ b/nptl/nptl-init.c
> @@ -32,7 +32,6 @@
>  #include <fork.h>
>  #include <version.h>
>  #include <shlib-compat.h>
> -#include <smp.h>
>  #include <lowlevellock.h>
>  #include <futex-internal.h>
>  #include <kernel-features.h>

Ok.

> @@ -346,9 +345,6 @@ __pthread_initialize_minimal_internal (void)
>      __libc_pthread_init (&__fork_generation, __reclaim_stacks,
>  			 ptr_pthread_functions);
>  
> -  /* Determine whether the machine is SMP or not.  */
> -  __is_smp = is_smp_system ();
> -
>  #if HAVE_TUNABLES
>    __pthread_tunables_init ();
>  #endif

Ok.

> diff --git a/nptl/pthreadP.h b/nptl/pthreadP.h
> index 710b21e890..686f54aa93 100644
> --- a/nptl/pthreadP.h
> +++ b/nptl/pthreadP.h
> @@ -208,9 +208,6 @@ extern void __default_pthread_attr_freeres (void) attribute_hidden;
>  extern size_t __static_tls_size attribute_hidden;
>  extern size_t __static_tls_align_m1 attribute_hidden;
>  
> -/* Flag whether the machine is SMP or not.  */
> -extern int __is_smp attribute_hidden;
> -
>  /* Thread descriptor handling.  */
>  extern list_t __stack_user;
>  hidden_proto (__stack_user)

Ok.

> diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c
> index 7858abd528..fac774e608 100644
> --- a/nptl/pthread_mutex_lock.c
> +++ b/nptl/pthread_mutex_lock.c
> @@ -120,9 +120,6 @@ __pthread_mutex_lock (pthread_mutex_t *mutex)
>    else if (__builtin_expect (PTHREAD_MUTEX_TYPE (mutex)
>  			  == PTHREAD_MUTEX_ADAPTIVE_NP, 1))
>      {
> -      if (! __is_smp)
> -	goto simple;
> -
>        if (LLL_MUTEX_TRYLOCK (mutex) != 0)
>  	{
>  	  int cnt = 0;

Ok.

> diff --git a/nptl/pthread_mutex_timedlock.c b/nptl/pthread_mutex_timedlock.c
> index fe9e651f6c..de88e9fc25 100644
> --- a/nptl/pthread_mutex_timedlock.c
> +++ b/nptl/pthread_mutex_timedlock.c
> @@ -113,9 +113,6 @@ __pthread_mutex_clocklock_common (pthread_mutex_t *mutex,
>  
>  
>      case PTHREAD_MUTEX_ADAPTIVE_NP:
> -      if (! __is_smp)
> -	goto simple;
> -
>        if (lll_trylock (mutex->__data.__lock) != 0)
>  	{
>  	  int cnt = 0;

Ok.

> diff --git a/nptl/smp.h b/nptl/smp.h
> deleted file mode 100644
> index 537e5e945c..0000000000
> --- a/nptl/smp.h
> +++ /dev/null
> @@ -1,27 +0,0 @@
> -/* Determine whether the host has multiple processors.  Stub version.
> -   Copyright (C) 1996-2020 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 Library General Public License as
> -   published by the Free Software Foundation; either version 2 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
> -   Library General Public License for more details.
> -
> -   You should have received a copy of the GNU Library General Public
> -   License along with the GNU C Library; see the file COPYING.LIB.  If
> -   not, see <https://www.gnu.org/licenses/>.  */
> -
> -/* Test whether the machine has more than one processor.  This is not the
> -   best test but good enough.  More complicated tests would require `malloc'
> -   which is not available at that time.  */
> -static inline int
> -is_smp_system (void)
> -{
> -  /* Assume all machines are SMP and/or CMT and/or SMT.  */
> -  return 1;
> -}

Ok.

> diff --git a/nptl/vars.c b/nptl/vars.c
> index 3696020145..2f52391dc2 100644
> --- a/nptl/vars.c
> +++ b/nptl/vars.c
> @@ -27,9 +27,6 @@ union pthread_attr_transparent __default_pthread_attr attribute_hidden;
>  /* Mutex protecting __default_pthread_attr.  */
>  int __default_pthread_attr_lock = LLL_LOCK_INITIALIZER;
>  
> -/* Flag whether the machine is SMP or not.  */
> -int __is_smp attribute_hidden;
> -
>  #ifndef TLS_MULTIPLE_THREADS_IN_TCB
>  /* Variable set to a nonzero value either if more than one thread runs or ran,
>     or if a single-threaded process is trying to cancel itself.  See

Ok.

> diff --git a/sysdeps/unix/sysv/linux/i386/smp.h b/sysdeps/unix/sysv/linux/i386/smp.h
> deleted file mode 100644
> index 85a630d048..0000000000
> --- a/sysdeps/unix/sysv/linux/i386/smp.h
> +++ /dev/null
> @@ -1,55 +0,0 @@
> -/* Determine whether the host has multiple processors.  Linux version.
> -   Copyright (C) 1996-2020 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 Library General Public License as
> -   published by the Free Software Foundation; either version 2 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
> -   Library General Public License for more details.
> -
> -   You should have received a copy of the GNU Library General Public
> -   License along with the GNU C Library; see the file COPYING.LIB.  If
> -   not, see <https://www.gnu.org/licenses/>.  */
> -
> -#include <errno.h>
> -#include <fcntl.h>
> -#include <string.h>
> -#include <sys/utsname.h>
> -#include <not-cancel.h>
> -
> -/* Test whether the machine has more than one processor.  This is not the
> -   best test but good enough.  More complicated tests would require `malloc'
> -   which is not available at that time.  */
> -static inline int
> -is_smp_system (void)
> -{
> -  union
> -  {
> -    struct utsname uts;
> -    char buf[512];
> -  } u;
> -  char *cp;
> -
> -  /* Try reading the number using `sysctl' first.  */
> -  if (__uname (&u.uts) == 0)
> -    cp = u.uts.version;
> -  else
> -    {
> -      /* This was not successful.  Now try reading the /proc filesystem.  */
> -      int fd = __open64_nocancel ("/proc/sys/kernel/version", O_RDONLY);
> -      if (__builtin_expect (fd, 0) == -1
> -	  || __read_nocancel (fd, u.buf, sizeof (u.buf)) <= 0)
> -	/* This also didn't work.  We give up and say it's a UP machine.  */
> -	u.buf[0] = '\0';
> -
> -      __close_nocancel_nostatus (fd);
> -      cp = u.buf;
> -    }
> -
> -  return strstr (cp, "SMP") != NULL;
> -}

Ok.

> diff --git a/sysdeps/unix/sysv/linux/sh/adaptive_spin_count.h b/sysdeps/unix/sysv/linux/sh/adaptive_spin_count.h
> new file mode 100644
> index 0000000000..3431cd3d8c
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/sh/adaptive_spin_count.h
> @@ -0,0 +1,20 @@
> +/* Maximum adaptive spin count default for sh.
> +   Copyright (C) 2020 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
> +   <https://www.gnu.org/licenses/>.  */
> +
> +/* Disable spinning because sh is always uniprocessor.  */
> +#define DEFAULT_ADAPTIVE_COUNT 0

Ok.  Maybe an option is dropping this optimization in favor a simplified
code base.

> diff --git a/sysdeps/unix/sysv/linux/sh/smp.h b/sysdeps/unix/sysv/linux/sh/smp.h
> deleted file mode 100644
> index 55efedc0ba..0000000000
> --- a/sysdeps/unix/sysv/linux/sh/smp.h
> +++ /dev/null
> @@ -1,23 +0,0 @@
> -/* Determine whether the host has multiple processors.  SH version.
> -   Copyright (C) 2002-2020 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 Library General Public License as
> -   published by the Free Software Foundation; either version 2 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
> -   Library General Public License for more details.
> -
> -   You should have received a copy of the GNU Library General Public
> -   License along with the GNU C Library; see the file COPYING.LIB.  If
> -   not, see <https://www.gnu.org/licenses/>.  */
> -
> -static inline int
> -is_smp_system (void)
> -{
> -  return 0;
> -}
> 

Ok.