diff mbox

[3/4] Enhance --enable-tunables to select tunables frontend at build time

Message ID 1479285306-11684-4-git-send-email-siddhesh@sourceware.org
State New
Headers show

Commit Message

Siddhesh Poyarekar Nov. 16, 2016, 8:35 a.m. UTC 
At the GNU Tools Cauldron 2016, the state of the current tunables
patchset was considered OK with the addition of a way to select the
frontend to be used for the tunables.  That is, to avoid being locked
in to one type of frontend initially, it should be possible to build
tunables with a different frontend with something as simple as a
configure switch.

To that effect, this patch enhances the --enable-tunables option to
accept more values than just 'yes' or 'no'.  The current frontend (and
default when enable-tunables is 'yes') is called 'valstring', to
select the frontend where a single environment variable is set to a
colon-separated value string.  More such frontends can be added in
future.

	* Makeconfig (have-tunables): Check for non-negative instead
	of positive.
	* configure.ac: Add 'valstring' as a valid value for
	--enable-tunables.
	* configure: Regenerate.
	* elf/Makefile (have-tunables): Check for non-negative instead
	of positive.
	(CPPFLAGS-dl-tunables.c): Define TUNABLES_FRONTEND for
	dl-tunables.c.
	* elf/dl-tunables.c (GLIBC_TUNABLES): Define only when
	TUNABLES_FRONTEND == TUNABLES_FRONTEND_valstring.
	(tunables_strdup): Likewise.
	(disable_tunables): Likewise.
	(parse_tunables): Likewise.
	(__tunables_init): Process GLIBC_TUNABLES envvar only when.
	TUNABLES_FRONTEND == TUNABLES_FRONTEND_valstring.
	* elf/dl-tunables.h (TUNABLES_FRONTEND_valstring): New macro.
	(TUNABLES_FRONTEND_yes): New macro, define as
	TUNABLES_FRONTEND_valstring by default.
	* manual/install.texi: Document new acceptable values for
	--enable-tunables.
	* INSTALL: Regenerate.
---
 INSTALL             | 15 ++++++++++++++-
 Makeconfig          |  4 ++--
 configure           |  3 ++-
 configure.ac        |  2 +-
 elf/Makefile        |  4 +++-
 elf/dl-tunables.c   | 12 +++++++++++-
 elf/dl-tunables.h   |  4 ++++
 manual/install.texi | 18 +++++++++++++++++-
 8 files changed, 54 insertions(+), 8 deletions(-)

Comments

Florian Weimer Dec. 27, 2016, 11:44 a.m. UTC | #1 
On 11/16/2016 09:35 AM, Siddhesh Poyarekar wrote:
> At the GNU Tools Cauldron 2016, the state of the current tunables
> patchset was considered OK with the addition of a way to select the
> frontend to be used for the tunables.  That is, to avoid being locked
> in to one type of frontend initially, it should be possible to build
> tunables with a different frontend with something as simple as a
> configure switch.
>
> To that effect, this patch enhances the --enable-tunables option to
> accept more values than just 'yes' or 'no'.  The current frontend (and
> default when enable-tunables is 'yes') is called 'valstring', to
> select the frontend where a single environment variable is set to a
> colon-separated value string.  More such frontends can be added in
> future.

I'm not sure if this patch makes sense at this point because without 
alternative frontends, it's impossible to tell if the current 
initialization sequence is sufficient.

For example, if we want to load a tunable configuration with very low 
cost, we could use ldconfig to pre-parse a configuration file and put it 
into /etc/ld.so.cache.  But we won't know if the current approach works 
until this is actually implemented.

Thanks,
Florian
Siddhesh Poyarekar Dec. 27, 2016, 9:10 p.m. UTC | #2 
On Tuesday 27 December 2016 05:14 PM, Florian Weimer wrote:
> I'm not sure if this patch makes sense at this point because without
> alternative frontends, it's impossible to tell if the current
> initialization sequence is sufficient.
> 
> For example, if we want to load a tunable configuration with very low
> cost, we could use ldconfig to pre-parse a configuration file and put it
> into /etc/ld.so.cache.  But we won't know if the current approach works
> until this is actually implemented.

The option --enable-tunables=... doesn't actually do anything beyond
explicitly naming the current tunables frontend implementation.  To
write a different frontend, one would not only have to add a new value
to the --enable-tunables=... option but also tweak the current
initialization sequence to suit its frontend without hurting existing
frontends.

I did not intend to make a framework to allow plugging in of different
frontends directly because from the discussions at Cauldron I concluded
that the primary reason for such a requirement was more to loosen the
guarantee of availability of a specific frontend than to allow
co-existence of different frontends at the same time.

Siddhesh
Florian Weimer Dec. 27, 2016, 9:15 p.m. UTC | #3 
On 12/27/2016 10:10 PM, Siddhesh Poyarekar wrote:
> On Tuesday 27 December 2016 05:14 PM, Florian Weimer wrote:
>> I'm not sure if this patch makes sense at this point because without
>> alternative frontends, it's impossible to tell if the current
>> initialization sequence is sufficient.
>>
>> For example, if we want to load a tunable configuration with very low
>> cost, we could use ldconfig to pre-parse a configuration file and put it
>> into /etc/ld.so.cache.  But we won't know if the current approach works
>> until this is actually implemented.
>
> The option --enable-tunables=... doesn't actually do anything beyond
> explicitly naming the current tunables frontend implementation.  To
> write a different frontend, one would not only have to add a new value
> to the --enable-tunables=... option but also tweak the current
> initialization sequence to suit its frontend without hurting existing
> frontends.

Okay.  I don't know what was decided at the Cauldron because it wasn't 
there.  The patch doesn't look burdensome going forward, so maybe we can 
keep it if it makes someone happy.

Thanks,
Florian
diff mbox

Patch

diff --git a/INSTALL b/INSTALL
index ccacccc..55f6a23 100644
--- a/INSTALL
+++ b/INSTALL
@@ -161,7 +161,20 @@  will be used, and CFLAGS sets optimization options for the compiler.
 '--enable-tunables'
      Tunables support allows additional library parameters to be
      customized at runtime.  This is an experimental feature and affects
-     startup time and is thus disabled by default.
+     startup time and is thus disabled by default.  This option can take
+     the following values:
+
+        * NO This is the default if the option is not passed to
+          configure.  This disables tunables.
+
+        * YES This is the default if the option is passed to configure.
+          This enables tunables and selects the default frontend
+          (currently VALSTRING).
+
+        * VALSTRING This enables tunables and selects the VALSTRING
+          frontend for tunables.  This frontend allows users to specify
+          tunables as a colon-separated list in a single environment
+          variable GLIBC_TUNABLES.
 
 '--build=BUILD-SYSTEM'
 '--host=HOST-SYSTEM'
diff --git a/Makeconfig b/Makeconfig
index d0eb832..09ddb12 100644
--- a/Makeconfig
+++ b/Makeconfig
@@ -884,7 +884,7 @@  CPPFLAGS = $(config-extra-cppflags) $(CPPUNDEFS) $(CPPFLAGS-config) \
 			 $(libof-$(<F)) $(libof-$(@F)),$(CPPFLAGS-$(lib))) \
 	   $(CPPFLAGS-$(<F)) $(CPPFLAGS-$(@F)) $(CPPFLAGS-$(basename $(@F)))
 
-ifeq (yes,$(have-tunables))
+ifneq (no,$(have-tunables))
 CPPFLAGS += -DTOP_NAMESPACE=glibc
 endif
 
@@ -1064,7 +1064,7 @@  endif
 
 # Build the tunables list header early since it could be used by any module in
 # glibc.
-ifeq (yes,$(have-tunables))
+ifneq (no,$(have-tunables))
 before-compile += $(common-objpfx)dl-tunable-list.h
 
 $(common-objpfx)dl-tunable-list.h: $(..)scripts/gen-tunables.awk \
diff --git a/configure b/configure
index cbd5fb3..35a9ecf 100755
--- a/configure
+++ b/configure
@@ -1445,7 +1445,8 @@  Optional Features:
   --disable-build-nscd    disable building and installing the nscd daemon
   --disable-nscd          library functions will not contact the nscd daemon
   --enable-pt_chown       Enable building and installing pt_chown
-  --enable-tunables       Enable tunables support
+  --enable-tunables       Enable tunables support. Known values are 'yes',
+                          'no' and 'valstring'
   --enable-mathvec        Enable building and installing mathvec [default
                           depends on architecture]
 
diff --git a/configure.ac b/configure.ac
index 3b7a0db..5e2c8ca 100644
--- a/configure.ac
+++ b/configure.ac
@@ -397,7 +397,7 @@  fi
 
 AC_ARG_ENABLE([tunables],
 	      [AS_HELP_STRING([--enable-tunables],
-	       [Enable tunables support])],
+	       [Enable tunables support. Known values are 'yes', 'no' and 'valstring'])],
 	      [have_tunables=$enableval],
 	      [have_tunables=no])
 AC_SUBST(have_tunables)
diff --git a/elf/Makefile b/elf/Makefile
index 477f8fc..34fc657 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -36,8 +36,10 @@  ifeq (yes,$(use-ldconfig))
 dl-routines += dl-cache
 endif
 
-ifeq (yes,$(have-tunables))
+ifneq (no,$(have-tunables))
 dl-routines += dl-tunables
+tunables-type = $(addprefix TUNABLES_FRONTEND_,$(have-tunables))
+CPPFLAGS-dl-tunables.c = -DTUNABLES_FRONTEND=$(tunables-type)
 endif
 
 all-dl-routines = $(dl-routines) $(sysdep-dl-routines)
diff --git a/elf/dl-tunables.c b/elf/dl-tunables.c
index 79ec8ef..128da29 100644
--- a/elf/dl-tunables.c
+++ b/elf/dl-tunables.c
@@ -30,7 +30,9 @@ 
 #define TUNABLES_INTERNAL 1
 #include "dl-tunables.h"
 
-#define GLIBC_TUNABLES "GLIBC_TUNABLES"
+#if TUNABLES_FRONTEND == TUNABLES_FRONTEND_valstring
+# define GLIBC_TUNABLES "GLIBC_TUNABLES"
+#endif
 
 /* Compare environment or tunable names, bounded by the name hardcoded in
    glibc.  */
@@ -48,6 +50,7 @@  is_name (const char *orig, const char *envname)
     return false;
 }
 
+#if TUNABLES_FRONTEND == TUNABLES_FRONTEND_valstring
 static char *
 tunables_strdup (const char *in)
 {
@@ -69,6 +72,7 @@  tunables_strdup (const char *in)
 
   return out;
 }
+#endif
 
 static char **
 get_next_env (char **envp, char **name, size_t *namelen, char **val)
@@ -234,6 +238,7 @@  tunable_initialize (tunable_t *cur, const char *strval)
     }
 }
 
+#if TUNABLES_FRONTEND == TUNABLES_FRONTEND_valstring
 static void
 parse_tunables (char *tunestr)
 {
@@ -299,6 +304,7 @@  parse_tunables (char *tunestr)
 	return;
     }
 }
+#endif
 
 static size_t
 min_strlen (const char *s)
@@ -319,6 +325,7 @@  disable_tunable (tunable_id_t id, char **envp)
   if (env_alias)
     tunables_unsetenv (envp, tunable_list[id].env_alias);
 
+#if TUNABLES_FRONTEND == TUNABLES_FRONTEND_valstring
   char *tunable = getenv (GLIBC_TUNABLES);
   const char *cmp = tunable_list[id].name;
   const size_t len = min_strlen (cmp);
@@ -335,6 +342,7 @@  disable_tunable (tunable_id_t id, char **envp)
 	}
       tunable++;
     }
+#endif
 }
 
 /* Disable the glibc.malloc.check tunable in SETUID/SETGID programs unless
@@ -365,6 +373,7 @@  __tunables_init (char **envp)
 
   while ((envp = get_next_env (envp, &envname, &len, &envval)) != NULL)
     {
+#if TUNABLES_FRONTEND == TUNABLES_FRONTEND_valstring
       if (is_name (GLIBC_TUNABLES, envname))
 	{
 	  char *val = tunables_strdup (envval);
@@ -372,6 +381,7 @@  __tunables_init (char **envp)
 	    parse_tunables (val);
 	  continue;
 	}
+#endif
 
       for (int i = 0; i < sizeof (tunable_list) / sizeof (tunable_t); i++)
 	{
diff --git a/elf/dl-tunables.h b/elf/dl-tunables.h
index 10a644b..27b1b64 100644
--- a/elf/dl-tunables.h
+++ b/elf/dl-tunables.h
@@ -75,4 +75,8 @@  extern void __tunable_set_val (tunable_id_t, void *, tunable_callback_t);
 /* Namespace sanity for callback functions.  Use this macro to keep the
    namespace of the modules clean.  */
 #define DL_TUNABLE_CALLBACK(__name) _dl_tunable_ ## __name
+
+# define TUNABLES_FRONTEND_valstring 1
+/* The default value for TUNABLES_FRONTEND.  */
+# define TUNABLES_FRONTEND_yes TUNABLES_FRONTEND_valstring
 #endif
diff --git a/manual/install.texi b/manual/install.texi
index ffc166d..e34c7bf 100644
--- a/manual/install.texi
+++ b/manual/install.texi
@@ -192,7 +192,23 @@  Use this option to disable the vector math library.
 @item --enable-tunables
 Tunables support allows additional library parameters to be customized at
 runtime.  This is an experimental feature and affects startup time and is thus
-disabled by default.
+disabled by default.  This option can take the following values:
+
+@itemize @bullet
+@item @var{no}
+This is the default if the option is not passed to configure. This disables
+tunables.
+
+@item @var{yes}
+This is the default if the option is passed to configure. This enables tunables
+and selects the default frontend (currently @var{valstring}).
+
+@item @var{valstring}
+This enables tunables and selects the @var{valstring} frontend for tunables.
+This frontend allows users to specify tunables as a colon-separated list in a
+single environment variable @var{GLIBC_TUNABLES}.
+
+@end itemize
 
 @item --build=@var{build-system}
 @itemx --host=@var{host-system}