[PATCH 1/3 V3] time: move timeconst.h into include/generated

[PATCH 1/3 V3] time: move timeconst.h into include/generated

[Nicholas Mc Guire]

kernel/time/timeconst.h is moved to include/generated/ and generated 
by the top level Kbuild. This allows using timeconst.h in an earlier
build stage.

Patch was build tested for:
  arm - imx_v6_v7_defconfig, vexpress_defconfig
  cris - etrax-100lx_v2_defconfig
  m68k - multi_defconfig
  mips32 - ar7_defconfig,
  mips64 - loongson3_defconfig 
  powerpc - 44x/virtex5_defconfig
  powerpc64 - powerpc64_defconfig
  sh - se7780_defconfig,
  sparc32 - sparc32_defconfig
  sparc64 - sparc64_defconfig
  x86 64 - x86_64_defconfig,

Patch is against 4.1-rc3 (localversion-next is -next-20150518)

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
---

Thanks to Joe Perches <joe@perches.com> for suggesting this approach 
and catching the unconditional rebuild (should be fixed here now 
properly) as well as for his review comments on the first attempts.

V3: minor change in top level Kbuild to make mips64 build correctly
    (timeconst.h added to dependency list of asm-offset.h)

 Kbuild                   |   34 +++++++++++++++++++++++++++-------
 kernel/time/Makefile     |   17 +----------------
 kernel/time/time.c       |    2 +-
 kernel/time/timeconst.bc |    3 ++-
 4 files changed, 31 insertions(+), 25 deletions(-)

diff --git a/Kbuild b/Kbuild
index 6f0d82a..df99a5f 100644
--- a/Kbuild
+++ b/Kbuild
@@ -2,8 +2,9 @@
 # Kbuild for top-level directory of the kernel
 # This file takes care of the following:
 # 1) Generate bounds.h
-# 2) Generate asm-offsets.h (may need bounds.h)
-# 3) Check for missing system calls
+# 2) Generate timeconst.h
+# 3) Generate asm-offsets.h (may need bounds.h and timeconst.h)
+# 4) Check for missing system calls
 
 # Default sed regexp - multiline due to syntax constraints
 define sed-y
@@ -47,7 +48,26 @@ $(obj)/$(bounds-file): kernel/bounds.s FORCE
 	$(call filechk,offsets,__LINUX_BOUNDS_H__)
 
 #####
-# 2) Generate asm-offsets.h
+# 2) Generate timeconst.h
+
+timeconst-file := include/generated/timeconst.h
+
+#always  += $(timeconst-file)
+targets += $(timeconst-file)
+
+quiet_cmd_gentimeconst = GEN     $@
+define cmd_gentimeconst
+	(echo $(CONFIG_HZ) | bc -q $< ) > $@
+endef
+define filechk_gentimeconst
+	(echo $(CONFIG_HZ) | bc -q $< )
+endef
+
+$(obj)/$(timeconst-file): kernel/time/timeconst.bc FORCE
+	$(call filechk,gentimeconst)
+
+#####
+# 3) Generate asm-offsets.h
 #
 
 offsets-file := include/generated/asm-offsets.h
@@ -57,7 +77,7 @@ targets += arch/$(SRCARCH)/kernel/asm-offsets.s
 
 # We use internal kbuild rules to avoid the "is up to date" message from make
 arch/$(SRCARCH)/kernel/asm-offsets.s: arch/$(SRCARCH)/kernel/asm-offsets.c \
-                                      $(obj)/$(bounds-file) FORCE
+                                      $(obj)/$(timeconst-file) $(obj)/$(bounds-file) FORCE
 	$(Q)mkdir -p $(dir $@)
 	$(call if_changed_dep,cc_s_c)
 
@@ -65,7 +85,7 @@ $(obj)/$(offsets-file): arch/$(SRCARCH)/kernel/asm-offsets.s FORCE
 	$(call filechk,offsets,__ASM_OFFSETS_H__)
 
 #####
-# 3) Check for missing system calls
+# 4) Check for missing system calls
 #
 
 always += missing-syscalls
@@ -77,5 +97,5 @@ quiet_cmd_syscalls = CALL    $<
 missing-syscalls: scripts/checksyscalls.sh $(offsets-file) FORCE
 	$(call cmd,syscalls)
 
-# Keep these two files during make clean
-no-clean-files := $(bounds-file) $(offsets-file)
+# Keep these three files during make clean
+no-clean-files := $(bounds-file) $(offsets-file) $(timeconst-file)
diff --git a/kernel/time/Makefile b/kernel/time/Makefile
index 01f0312..ffc4cc3 100644
--- a/kernel/time/Makefile
+++ b/kernel/time/Makefile
@@ -13,19 +13,4 @@ obj-$(CONFIG_TIMER_STATS)			+= timer_stats.o
 obj-$(CONFIG_DEBUG_FS)				+= timekeeping_debug.o
 obj-$(CONFIG_TEST_UDELAY)			+= test_udelay.o
 
-$(obj)/time.o: $(obj)/timeconst.h
-
-quiet_cmd_hzfile = HZFILE  $@
-      cmd_hzfile = echo "hz=$(CONFIG_HZ)" > $@
-
-targets += hz.bc
-$(obj)/hz.bc: $(objtree)/include/config/hz.h FORCE
-	$(call if_changed,hzfile)
-
-quiet_cmd_bc  = BC      $@
-      cmd_bc  = bc -q $(filter-out FORCE,$^) > $@
-
-targets += timeconst.h
-$(obj)/timeconst.h: $(obj)/hz.bc $(src)/timeconst.bc FORCE
-	$(call if_changed,bc)
-
+$(obj)/time.o: $(objtree)/include/config/
diff --git a/kernel/time/time.c b/kernel/time/time.c
index 2c85b77..4fa1d26 100644
--- a/kernel/time/time.c
+++ b/kernel/time/time.c
@@ -41,7 +41,7 @@
 #include <asm/uaccess.h>
 #include <asm/unistd.h>
 
-#include "timeconst.h"
+#include <generated/timeconst.h>
 #include "timekeeping.h"
 
 /*
diff --git a/kernel/time/timeconst.bc b/kernel/time/timeconst.bc
index 511bdf2..c7388de 100644
--- a/kernel/time/timeconst.bc
+++ b/kernel/time/timeconst.bc
@@ -50,7 +50,7 @@ define timeconst(hz) {
 	print "#include <linux/types.h>\n\n"
 
 	print "#if HZ != ", hz, "\n"
-	print "#error \qkernel/timeconst.h has the wrong HZ value!\q\n"
+	print "#error \qinclude/generated/timeconst.h has the wrong HZ value!\q\n"
 	print "#endif\n\n"
 
 	if (hz < 2) {
@@ -105,4 +105,5 @@ define timeconst(hz) {
 	halt
 }
 
+hz = read();
 timeconst(hz)
-- 
1.7.10.4

[PATCH 2/3 V3] time: refactor msecs_to_jiffies

[Nicholas Mc Guire]

Refactor the msecs_to_jiffies conditional code part in time.c and 
jiffies.h putting it into conditional functions rather than #ifdefs
to improve readability.

Patch was build tested for:
  arm - imx_v6_v7_defconfig, vexpress_defconfig
  cris - etrax-100lx_v2_defconfig
  m68k - multi_defconfig
  mips32 - ar7_defconfig,
  mips64 - loongson3_defconfig 
  powerpc - 44x/virtex5_defconfig
  powerpc64 - powerpc64_defconfig
  sh - se7780_defconfig,
  sparc32 - sparc32_defconfig
  sparc64 - sparc64_defconfig
  x86 64 - x86_64_defconfig,
and boot/run tested for
  x86 64 - x86_64_defconfig on an i3

Patch is against 4.1-rc3 (localversion-next is -next-20150518)

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
---

Thanks to Joe Perches <joe@perches.com> for suggesting this approach 
and for his review comments on the first attempts and for his simple
test-case that helped after I confused my self with .lst files.

V3: refactoring of time.c/jiffies.h  as requested by Thomas Gleixner
    <tglx@linutronix.de> without actually adding the builtin_constant_p()
    check

 include/linux/jiffies.h |   64 ++++++++++++++++++++++++++++++++++++++++++++++-
 kernel/time/time.c      |   59 ++++++++++++++-----------------------------
 2 files changed, 82 insertions(+), 41 deletions(-)

diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
index c367cbd..b41e026e 100644
--- a/include/linux/jiffies.h
+++ b/include/linux/jiffies.h
@@ -7,6 +7,7 @@
 #include <linux/time.h>
 #include <linux/timex.h>
 #include <asm/param.h>			/* for HZ */
+#include <generated/timeconst.h>
 
 /*
  * The following defines establish the engineering parameters of the PLL
@@ -288,7 +289,68 @@ static inline u64 jiffies_to_nsecs(const unsigned long j)
 	return (u64)jiffies_to_usecs(j) * NSEC_PER_USEC;
 }
 
-extern unsigned long msecs_to_jiffies(const unsigned int m);
+extern unsigned long __msecs_to_jiffies(const unsigned int m);
+#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
+/*
+ * HZ is equal to or smaller than 1000, and 1000 is a nice round
+ * multiple of HZ, divide with the factor between them, but round
+ * upwards:
+ */
+static inline unsigned long _msecs_to_jiffies(const unsigned int m)
+{
+		return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
+}
+#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
+/*
+ * HZ is larger than 1000, and HZ is a nice round multiple of 1000 -
+ * simply multiply with the factor between them.
+ *
+ * But first make sure the multiplication result cannot overflow:
+ */
+static inline unsigned long _msecs_to_jiffies(const unsigned int m)
+{
+		if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
+			return MAX_JIFFY_OFFSET;
+		return m * (HZ / MSEC_PER_SEC);
+}
+#else
+/*
+ * Generic case - multiply, round and divide. But first check that if
+ * we are doing a net multiplication, that we wouldn't overflow:
+ */
+static inline unsigned long _msecs_to_jiffies(const unsigned int m)
+{
+		if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
+			return MAX_JIFFY_OFFSET;
+
+		return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
+			>> MSEC_TO_HZ_SHR32;
+}
+#endif
+/**
+ * msecs_to_jiffies: - convert milliseconds to jiffies
+ * @m:	time in milliseconds
+ *
+ * conversion is done as follows:
+ *
+ * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
+ *
+ * - 'too large' values [that would result in larger than
+ *   MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
+ *
+ * - all other values are converted to jiffies by either multiplying
+ *   the input value by a factor or dividing it with a factor and
+ *   handling any 32-bit overflows.
+ *   for the details see __msecs_to_jiffies()
+ *
+ * the HZ range specific helpers _msecs_to_jiffies() are called from
+ * __msecs_to_jiffies().
+ */
+static inline unsigned long msecs_to_jiffies(const unsigned int m)
+{
+	return __msecs_to_jiffies(m);
+}
+
 extern unsigned long usecs_to_jiffies(const unsigned int u);
 extern unsigned long timespec_to_jiffies(const struct timespec *value);
 extern void jiffies_to_timespec(const unsigned long jiffies,
diff --git a/kernel/time/time.c b/kernel/time/time.c
index 4fa1d26..884bb8e 100644
--- a/kernel/time/time.c
+++ b/kernel/time/time.c
@@ -483,9 +483,11 @@ struct timespec64 ns_to_timespec64(const s64 nsec)
 }
 EXPORT_SYMBOL(ns_to_timespec64);
 #endif
-/*
- * When we convert to jiffies then we interpret incoming values
- * the following way:
+/**
+ * msecs_to_jiffies: - convert milliseconds to jiffies
+ * @m:	time in milliseconds
+ *
+ * conversion is done as follows:
  *
  * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
  *
@@ -493,51 +495,28 @@ EXPORT_SYMBOL(ns_to_timespec64);
  *   MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
  *
  * - all other values are converted to jiffies by either multiplying
- *   the input value by a factor or dividing it with a factor
- *
- * We must also be careful about 32-bit overflows.
+ *   the input value by a factor or dividing it with a factor and
+ *   handling any 32-bit overflows.
+ *   for the details see __msecs_to_jiffies()
+ *
+ * msecs_to_jiffies() checks for the passed in value being a constant
+ * via __builtin_constant_p() allowing gcc to eliminate most of the
+ * code, __msecs_to_jiffies() is called if the value passed does not
+ * allow constant folding and the actual conversion must be done at
+ * runtime.
+ * the _msecs_to_jiffies helpers are the HZ dependent conversion
+ * routines found in include/linux/jiffies.h
  */
-unsigned long msecs_to_jiffies(const unsigned int m)
+unsigned long __msecs_to_jiffies(const unsigned int m)
 {
 	/*
 	 * Negative value, means infinite timeout:
 	 */
 	if ((int)m < 0)
 		return MAX_JIFFY_OFFSET;
-
-#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
-	/*
-	 * HZ is equal to or smaller than 1000, and 1000 is a nice
-	 * round multiple of HZ, divide with the factor between them,
-	 * but round upwards:
-	 */
-	return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
-#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
-	/*
-	 * HZ is larger than 1000, and HZ is a nice round multiple of
-	 * 1000 - simply multiply with the factor between them.
-	 *
-	 * But first make sure the multiplication result cannot
-	 * overflow:
-	 */
-	if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
-		return MAX_JIFFY_OFFSET;
-
-	return m * (HZ / MSEC_PER_SEC);
-#else
-	/*
-	 * Generic case - multiply, round and divide. But first
-	 * check that if we are doing a net multiplication, that
-	 * we wouldn't overflow:
-	 */
-	if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
-		return MAX_JIFFY_OFFSET;
-
-	return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
-		>> MSEC_TO_HZ_SHR32;
-#endif
+	return _msecs_to_jiffies(m);
 }
-EXPORT_SYMBOL(msecs_to_jiffies);
+EXPORT_SYMBOL(__msecs_to_jiffies);
 
 unsigned long usecs_to_jiffies(const unsigned int u)
 {
-- 
1.7.10.4

[PATCH 3/3 V3] time: allow gcc to fold constants when possible

[Nicholas Mc Guire]

To allow constant folding in msecs_to_jiffies() conditionally calls
the HZ dependent _msecs_to_jiffies() helpers or, when gcc can not
figure out constant folding, __msecs_to_jiffies which is the renamed 
original msecs_to_jiffies() function. 

Patch was build tested for:
  arm - imx_v6_v7_defconfig, vexpress_defconfig
  cris - etrax-100lx_v2_defconfig
  m68k - multi_defconfig
  mips32 - ar7_defconfig,
  mips64 - loongson3_defconfig
  powerpc - 44x/virtex5_defconfig
  powerpc64 - powerpc64_defconfig
  sh - se7780_defconfig,
  sparc32 - sparc32_defconfig
  sparc64 - sparc64_defconfig
  x86 64 - x86_64_defconfig,
boot and run testing:
  x86 64 - x86_64_defconfig i3

Patch is against 4.1-rc3 (localversion-next is -next-20150518)

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
---

Thanks to Joe Perches <joe@perches.com> for suggesting this approach 
and for his review comments on the first attempts.

 include/linux/jiffies.h |   17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
index b41e026e..e96996a 100644
--- a/include/linux/jiffies.h
+++ b/include/linux/jiffies.h
@@ -343,12 +343,24 @@ static inline unsigned long _msecs_to_jiffies(const unsigned int m)
  *   handling any 32-bit overflows.
  *   for the details see __msecs_to_jiffies()
  *
- * the HZ range specific helpers _msecs_to_jiffies() are called from
- * __msecs_to_jiffies().
+ * msecs_to_jiffies() checks for the passed in value being a constant
+ * via __builtin_constant_p() allowing gcc to eliminate most of the
+ * code, __msecs_to_jiffies() is called if the value passed does not
+ * allow constant folding and the actual conversion must be done at
+ * runtime.
+ * the HZ range specific helpers _msecs_to_jiffies() are called both
+ * directly here and from __msecs_to_jiffies() in the case where
+ * constant folding is not possible.
  */
 static inline unsigned long msecs_to_jiffies(const unsigned int m)
 {
-	return __msecs_to_jiffies(m);
+	if (__builtin_constant_p(m)) {
+		if ((int)m < 0)
+			return MAX_JIFFY_OFFSET;
+		return _msecs_to_jiffies(m);
+	} else {
+		return __msecs_to_jiffies(m);
+	}
 }
 
 extern unsigned long usecs_to_jiffies(const unsigned int u);
-- 
1.7.10.4

[tip:timers/core] time: Move timeconst.h into include/generated

[tip-bot for Nicholas Mc Guire]

Commit-ID:  0a227985d4a993a322ff72ecbaeee2611d624216
Gitweb:     http://git.kernel.org/tip/0a227985d4a993a322ff72ecbaeee2611d624216
Author:     Nicholas Mc Guire <hofrat@osadl.org>
AuthorDate: Mon, 18 May 2015 14:19:12 +0200
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Tue, 19 May 2015 15:13:45 +0200

time: Move timeconst.h into include/generated

kernel/time/timeconst.h is moved to include/generated/ and generated 
by the top level Kbuild. This allows using timeconst.h in an earlier
build stage.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Cc: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Joe Perches <joe@perches.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Andrew Hunter <ahh@google.com>
Cc: Paul Turner <pjt@google.com>
Cc: Michal Marek <mmarek@suse.cz>
Link: http://lkml.kernel.org/r/1431951554-5563-1-git-send-email-hofrat@osadl.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 Kbuild                   | 34 +++++++++++++++++++++++++++-------
 kernel/time/Makefile     | 17 +----------------
 kernel/time/time.c       |  2 +-
 kernel/time/timeconst.bc |  3 ++-
 4 files changed, 31 insertions(+), 25 deletions(-)

diff --git a/Kbuild b/Kbuild
index 6f0d82a..df99a5f 100644
--- a/Kbuild
+++ b/Kbuild
@@ -2,8 +2,9 @@
 # Kbuild for top-level directory of the kernel
 # This file takes care of the following:
 # 1) Generate bounds.h
-# 2) Generate asm-offsets.h (may need bounds.h)
-# 3) Check for missing system calls
+# 2) Generate timeconst.h
+# 3) Generate asm-offsets.h (may need bounds.h and timeconst.h)
+# 4) Check for missing system calls
 
 # Default sed regexp - multiline due to syntax constraints
 define sed-y
@@ -47,7 +48,26 @@ $(obj)/$(bounds-file): kernel/bounds.s FORCE
 	$(call filechk,offsets,__LINUX_BOUNDS_H__)
 
 #####
-# 2) Generate asm-offsets.h
+# 2) Generate timeconst.h
+
+timeconst-file := include/generated/timeconst.h
+
+#always  += $(timeconst-file)
+targets += $(timeconst-file)
+
+quiet_cmd_gentimeconst = GEN     $@
+define cmd_gentimeconst
+	(echo $(CONFIG_HZ) | bc -q $< ) > $@
+endef
+define filechk_gentimeconst
+	(echo $(CONFIG_HZ) | bc -q $< )
+endef
+
+$(obj)/$(timeconst-file): kernel/time/timeconst.bc FORCE
+	$(call filechk,gentimeconst)
+
+#####
+# 3) Generate asm-offsets.h
 #
 
 offsets-file := include/generated/asm-offsets.h
@@ -57,7 +77,7 @@ targets += arch/$(SRCARCH)/kernel/asm-offsets.s
 
 # We use internal kbuild rules to avoid the "is up to date" message from make
 arch/$(SRCARCH)/kernel/asm-offsets.s: arch/$(SRCARCH)/kernel/asm-offsets.c \
-                                      $(obj)/$(bounds-file) FORCE
+                                      $(obj)/$(timeconst-file) $(obj)/$(bounds-file) FORCE
 	$(Q)mkdir -p $(dir $@)
 	$(call if_changed_dep,cc_s_c)
 
@@ -65,7 +85,7 @@ $(obj)/$(offsets-file): arch/$(SRCARCH)/kernel/asm-offsets.s FORCE
 	$(call filechk,offsets,__ASM_OFFSETS_H__)
 
 #####
-# 3) Check for missing system calls
+# 4) Check for missing system calls
 #
 
 always += missing-syscalls
@@ -77,5 +97,5 @@ quiet_cmd_syscalls = CALL    $<
 missing-syscalls: scripts/checksyscalls.sh $(offsets-file) FORCE
 	$(call cmd,syscalls)
 
-# Keep these two files during make clean
-no-clean-files := $(bounds-file) $(offsets-file)
+# Keep these three files during make clean
+no-clean-files := $(bounds-file) $(offsets-file) $(timeconst-file)
diff --git a/kernel/time/Makefile b/kernel/time/Makefile
index 01f0312..ffc4cc3 100644
--- a/kernel/time/Makefile
+++ b/kernel/time/Makefile
@@ -13,19 +13,4 @@ obj-$(CONFIG_TIMER_STATS)			+= timer_stats.o
 obj-$(CONFIG_DEBUG_FS)				+= timekeeping_debug.o
 obj-$(CONFIG_TEST_UDELAY)			+= test_udelay.o
 
-$(obj)/time.o: $(obj)/timeconst.h
-
-quiet_cmd_hzfile = HZFILE  $@
-      cmd_hzfile = echo "hz=$(CONFIG_HZ)" > $@
-
-targets += hz.bc
-$(obj)/hz.bc: $(objtree)/include/config/hz.h FORCE
-	$(call if_changed,hzfile)
-
-quiet_cmd_bc  = BC      $@
-      cmd_bc  = bc -q $(filter-out FORCE,$^) > $@
-
-targets += timeconst.h
-$(obj)/timeconst.h: $(obj)/hz.bc $(src)/timeconst.bc FORCE
-	$(call if_changed,bc)
-
+$(obj)/time.o: $(objtree)/include/config/
diff --git a/kernel/time/time.c b/kernel/time/time.c
index 2c85b77..4fa1d26 100644
--- a/kernel/time/time.c
+++ b/kernel/time/time.c
@@ -41,7 +41,7 @@
 #include <asm/uaccess.h>
 #include <asm/unistd.h>
 
-#include "timeconst.h"
+#include <generated/timeconst.h>
 #include "timekeeping.h"
 
 /*
diff --git a/kernel/time/timeconst.bc b/kernel/time/timeconst.bc
index 511bdf2..c7388de 100644
--- a/kernel/time/timeconst.bc
+++ b/kernel/time/timeconst.bc
@@ -50,7 +50,7 @@ define timeconst(hz) {
 	print "#include <linux/types.h>\n\n"
 
 	print "#if HZ != ", hz, "\n"
-	print "#error \qkernel/timeconst.h has the wrong HZ value!\q\n"
+	print "#error \qinclude/generated/timeconst.h has the wrong HZ value!\q\n"
 	print "#endif\n\n"
 
 	if (hz < 2) {
@@ -105,4 +105,5 @@ define timeconst(hz) {
 	halt
 }
 
+hz = read();
 timeconst(hz)

[tip:timers/core] time: Refactor msecs_to_jiffies

[tip-bot for Nicholas Mc Guire]

Commit-ID:  ca42aaf0c8616cde6161ea4391dff364efeee46a
Gitweb:     http://git.kernel.org/tip/ca42aaf0c8616cde6161ea4391dff364efeee46a
Author:     Nicholas Mc Guire <hofrat@osadl.org>
AuthorDate: Mon, 18 May 2015 14:19:13 +0200
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Tue, 19 May 2015 15:13:46 +0200

time: Refactor msecs_to_jiffies

Refactor the msecs_to_jiffies conditional code part in time.c and 
jiffies.h putting it into conditional functions rather than #ifdefs
to improve readability.

[ tglx: Verified that there is no binary code change ]

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Cc: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Joe Perches <joe@perches.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Andrew Hunter <ahh@google.com>
Cc: Paul Turner <pjt@google.com>
Cc: Michal Marek <mmarek@suse.cz>
Link: http://lkml.kernel.org/r/1431951554-5563-2-git-send-email-hofrat@osadl.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 include/linux/jiffies.h | 64 ++++++++++++++++++++++++++++++++++++++++++++++++-
 kernel/time/time.c      | 59 +++++++++++++++------------------------------
 2 files changed, 82 insertions(+), 41 deletions(-)

diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
index c367cbd..9527ddb 100644
--- a/include/linux/jiffies.h
+++ b/include/linux/jiffies.h
@@ -7,6 +7,7 @@
 #include <linux/time.h>
 #include <linux/timex.h>
 #include <asm/param.h>			/* for HZ */
+#include <generated/timeconst.h>
 
 /*
  * The following defines establish the engineering parameters of the PLL
@@ -288,7 +289,68 @@ static inline u64 jiffies_to_nsecs(const unsigned long j)
 	return (u64)jiffies_to_usecs(j) * NSEC_PER_USEC;
 }
 
-extern unsigned long msecs_to_jiffies(const unsigned int m);
+extern unsigned long __msecs_to_jiffies(const unsigned int m);
+#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
+/*
+ * HZ is equal to or smaller than 1000, and 1000 is a nice round
+ * multiple of HZ, divide with the factor between them, but round
+ * upwards:
+ */
+static inline unsigned long _msecs_to_jiffies(const unsigned int m)
+{
+		return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
+}
+#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
+/*
+ * HZ is larger than 1000, and HZ is a nice round multiple of 1000 -
+ * simply multiply with the factor between them.
+ *
+ * But first make sure the multiplication result cannot overflow:
+ */
+static inline unsigned long _msecs_to_jiffies(const unsigned int m)
+{
+		if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
+			return MAX_JIFFY_OFFSET;
+		return m * (HZ / MSEC_PER_SEC);
+}
+#else
+/*
+ * Generic case - multiply, round and divide. But first check that if
+ * we are doing a net multiplication, that we wouldn't overflow:
+ */
+static inline unsigned long _msecs_to_jiffies(const unsigned int m)
+{
+		if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
+			return MAX_JIFFY_OFFSET;
+
+		return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
+			>> MSEC_TO_HZ_SHR32;
+}
+#endif
+/**
+ * msecs_to_jiffies: - convert milliseconds to jiffies
+ * @m:	time in milliseconds
+ *
+ * conversion is done as follows:
+ *
+ * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
+ *
+ * - 'too large' values [that would result in larger than
+ *   MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
+ *
+ * - all other values are converted to jiffies by either multiplying
+ *   the input value by a factor or dividing it with a factor and
+ *   handling any 32-bit overflows.
+ *   for the details see __msecs_to_jiffies()
+ *
+ * the HZ range specific helpers _msecs_to_jiffies() are called from
+ * __msecs_to_jiffies().
+ */
+static inline unsigned long msecs_to_jiffies(const unsigned int m)
+{
+	return __msecs_to_jiffies(m);
+}
+
 extern unsigned long usecs_to_jiffies(const unsigned int u);
 extern unsigned long timespec_to_jiffies(const struct timespec *value);
 extern void jiffies_to_timespec(const unsigned long jiffies,
diff --git a/kernel/time/time.c b/kernel/time/time.c
index 4fa1d26..c42c2c3 100644
--- a/kernel/time/time.c
+++ b/kernel/time/time.c
@@ -483,9 +483,11 @@ struct timespec64 ns_to_timespec64(const s64 nsec)
 }
 EXPORT_SYMBOL(ns_to_timespec64);
 #endif
-/*
- * When we convert to jiffies then we interpret incoming values
- * the following way:
+/**
+ * msecs_to_jiffies: - convert milliseconds to jiffies
+ * @m:	time in milliseconds
+ *
+ * conversion is done as follows:
  *
  * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
  *
@@ -493,51 +495,28 @@ EXPORT_SYMBOL(ns_to_timespec64);
  *   MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
  *
  * - all other values are converted to jiffies by either multiplying
- *   the input value by a factor or dividing it with a factor
- *
- * We must also be careful about 32-bit overflows.
+ *   the input value by a factor or dividing it with a factor and
+ *   handling any 32-bit overflows.
+ *   for the details see __msecs_to_jiffies()
+ *
+ * msecs_to_jiffies() checks for the passed in value being a constant
+ * via __builtin_constant_p() allowing gcc to eliminate most of the
+ * code, __msecs_to_jiffies() is called if the value passed does not
+ * allow constant folding and the actual conversion must be done at
+ * runtime.
+ * the _msecs_to_jiffies helpers are the HZ dependent conversion
+ * routines found in include/linux/jiffies.h
  */
-unsigned long msecs_to_jiffies(const unsigned int m)
+unsigned long __msecs_to_jiffies(const unsigned int m)
 {
 	/*
 	 * Negative value, means infinite timeout:
 	 */
 	if ((int)m < 0)
 		return MAX_JIFFY_OFFSET;
-
-#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
-	/*
-	 * HZ is equal to or smaller than 1000, and 1000 is a nice
-	 * round multiple of HZ, divide with the factor between them,
-	 * but round upwards:
-	 */
-	return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
-#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
-	/*
-	 * HZ is larger than 1000, and HZ is a nice round multiple of
-	 * 1000 - simply multiply with the factor between them.
-	 *
-	 * But first make sure the multiplication result cannot
-	 * overflow:
-	 */
-	if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
-		return MAX_JIFFY_OFFSET;
-
-	return m * (HZ / MSEC_PER_SEC);
-#else
-	/*
-	 * Generic case - multiply, round and divide. But first
-	 * check that if we are doing a net multiplication, that
-	 * we wouldn't overflow:
-	 */
-	if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
-		return MAX_JIFFY_OFFSET;
-
-	return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
-		>> MSEC_TO_HZ_SHR32;
-#endif
+	return _msecs_to_jiffies(m);
 }
-EXPORT_SYMBOL(msecs_to_jiffies);
+EXPORT_SYMBOL(__msecs_to_jiffies);
 
 unsigned long usecs_to_jiffies(const unsigned int u)
 {

[tip:timers/core] time: Allow gcc to fold constants when possible

[tip-bot for Nicholas Mc Guire]

Commit-ID:  daa67b4b70568a07fef3cffacb2055891bf42ddb
Gitweb:     http://git.kernel.org/tip/daa67b4b70568a07fef3cffacb2055891bf42ddb
Author:     Nicholas Mc Guire <hofrat@osadl.org>
AuthorDate: Mon, 18 May 2015 14:19:14 +0200
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Tue, 19 May 2015 15:14:16 +0200

time: Allow gcc to fold constants when possible

To allow constant folding in msecs_to_jiffies() conditionally calls
the HZ dependent _msecs_to_jiffies() helpers or, when gcc can not
figure out constant folding, __msecs_to_jiffies which is the renamed
original msecs_to_jiffies() function.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Cc: Masahiro Yamada <yamada.m@jp.panasonic.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Joe Perches <joe@perches.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Andrew Hunter <ahh@google.com>
Cc: Paul Turner <pjt@google.com>
Cc: Michal Marek <mmarek@suse.cz>
Link: http://lkml.kernel.org/r/1431951554-5563-3-git-send-email-hofrat@osadl.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 include/linux/jiffies.h | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
index 9527ddb..5e75af6 100644
--- a/include/linux/jiffies.h
+++ b/include/linux/jiffies.h
@@ -343,12 +343,24 @@ static inline unsigned long _msecs_to_jiffies(const unsigned int m)
  *   handling any 32-bit overflows.
  *   for the details see __msecs_to_jiffies()
  *
- * the HZ range specific helpers _msecs_to_jiffies() are called from
- * __msecs_to_jiffies().
+ * msecs_to_jiffies() checks for the passed in value being a constant
+ * via __builtin_constant_p() allowing gcc to eliminate most of the
+ * code, __msecs_to_jiffies() is called if the value passed does not
+ * allow constant folding and the actual conversion must be done at
+ * runtime.
+ * the HZ range specific helpers _msecs_to_jiffies() are called both
+ * directly here and from __msecs_to_jiffies() in the case where
+ * constant folding is not possible.
  */
 static inline unsigned long msecs_to_jiffies(const unsigned int m)
 {
-	return __msecs_to_jiffies(m);
+	if (__builtin_constant_p(m)) {
+		if ((int)m < 0)
+			return MAX_JIFFY_OFFSET;
+		return _msecs_to_jiffies(m);
+	} else {
+		return __msecs_to_jiffies(m);
+	}
 }
 
 extern unsigned long usecs_to_jiffies(const unsigned int u);

Re: [tip:timers/core] time: Refactor msecs_to_jiffies

[Joe Perches]

On Tue, 2015-05-19 at 06:36 -0700, tip-bot for Nicholas Mc Guire wrote:
> Refactor the msecs_to_jiffies conditional code part in time.c and 
> jiffies.h putting it into conditional functions rather than #ifdefs
> to improve readability.
[]
> diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
[]
> +static inline unsigned long _msecs_to_jiffies(const unsigned int m)
> +{
> +		return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
> +}
> +#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
> +/*
> + * HZ is larger than 1000, and HZ is a nice round multiple of 1000 -
> + * simply multiply with the factor between them.
> + *
> + * But first make sure the multiplication result cannot overflow:
> + */
> +static inline unsigned long _msecs_to_jiffies(const unsigned int m)
> +{
> +		if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
> +			return MAX_JIFFY_OFFSET;
> +		return m * (HZ / MSEC_PER_SEC);
> +}
> +#else
> +/*
> + * Generic case - multiply, round and divide. But first check that if
> + * we are doing a net multiplication, that we wouldn't overflow:
> + */
> +static inline unsigned long _msecs_to_jiffies(const unsigned int m)
> +{
> +		if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
> +			return MAX_JIFFY_OFFSET;
> +
> +		return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
> +			>> MSEC_TO_HZ_SHR32;
> +}
> +#endif

It'd be nicer to remove 1 level of unnecessary tab indentation in
all the _msecs_to_jiffies functions here.

Re: [tip:timers/core] time: Refactor msecs_to_jiffies

[Nicholas Mc Guire]

On Tue, 19 May 2015, Joe Perches wrote:

> On Tue, 2015-05-19 at 06:36 -0700, tip-bot for Nicholas Mc Guire wrote:
> > Refactor the msecs_to_jiffies conditional code part in time.c and 
> > jiffies.h putting it into conditional functions rather than #ifdefs
> > to improve readability.
> []
> > diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
> []
> > +static inline unsigned long _msecs_to_jiffies(const unsigned int m)
> > +{
> > +		return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
> > +}
> > +#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
> > +/*
> > + * HZ is larger than 1000, and HZ is a nice round multiple of 1000 -
> > + * simply multiply with the factor between them.
> > + *
> > + * But first make sure the multiplication result cannot overflow:
> > + */
> > +static inline unsigned long _msecs_to_jiffies(const unsigned int m)
> > +{
> > +		if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
> > +			return MAX_JIFFY_OFFSET;
> > +		return m * (HZ / MSEC_PER_SEC);
> > +}
> > +#else
> > +/*
> > + * Generic case - multiply, round and divide. But first check that if
> > + * we are doing a net multiplication, that we wouldn't overflow:
> > + */
> > +static inline unsigned long _msecs_to_jiffies(const unsigned int m)
> > +{
> > +		if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
> > +			return MAX_JIFFY_OFFSET;
> > +
> > +		return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
> > +			>> MSEC_TO_HZ_SHR32;
> > +}
> > +#endif
> 
> It'd be nicer to remove 1 level of unnecessary tab indentation in
> all the _msecs_to_jiffies functions here.
>
oops - sorry - no idea how I did that - will fix up and resend

thx!
hofrat 

Re: [tip:timers/core] time: Refactor msecs_to_jiffies

[Thomas Gleixner]

On Tue, 19 May 2015, Joe Perches wrote:
> On Tue, 2015-05-19 at 06:36 -0700, tip-bot for Nicholas Mc Guire wrote:
> > Refactor the msecs_to_jiffies conditional code part in time.c and 
> > jiffies.h putting it into conditional functions rather than #ifdefs
> > to improve readability.
> []
> > diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h
> []
> > +static inline unsigned long _msecs_to_jiffies(const unsigned int m)
> > +{
> > +		return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
> > +}
> > +#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
> > +/*
> > + * HZ is larger than 1000, and HZ is a nice round multiple of 1000 -
> > + * simply multiply with the factor between them.
> > + *
> > + * But first make sure the multiplication result cannot overflow:
> > + */
> > +static inline unsigned long _msecs_to_jiffies(const unsigned int m)
> > +{
> > +		if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
> > +			return MAX_JIFFY_OFFSET;
> > +		return m * (HZ / MSEC_PER_SEC);
> > +}
> > +#else
> > +/*
> > + * Generic case - multiply, round and divide. But first check that if
> > + * we are doing a net multiplication, that we wouldn't overflow:
> > + */
> > +static inline unsigned long _msecs_to_jiffies(const unsigned int m)
> > +{
> > +		if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
> > +			return MAX_JIFFY_OFFSET;
> > +
> > +		return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
> > +			>> MSEC_TO_HZ_SHR32;
> > +}
> > +#endif
> 
> It'd be nicer to remove 1 level of unnecessary tab indentation in
> all the _msecs_to_jiffies functions here.

Indeed. I wanted to fix that up before applying and then forgot
again....

Thanks,

	tglx

Re: [tip:timers/core] time: Refactor msecs_to_jiffies

[Thomas Gleixner]

On Tue, 19 May 2015, Nicholas Mc Guire wrote:
> >
> oops - sorry - no idea how I did that - will fix up and resend

No. It's applied already, so we need to fix it with a delta patch,
which I pushed out already.

Thanks,

	tglx

Re: [tip:timers/core] time: Refactor msecs_to_jiffies

[Nicholas Mc Guire]

On Tue, 19 May 2015, Thomas Gleixner wrote:

> On Tue, 19 May 2015, Nicholas Mc Guire wrote:
> > >
> > oops - sorry - no idea how I did that - will fix up and resend
> 
> No. It's applied already, so we need to fix it with a delta patch,
> which I pushed out already.
>
ok - many thanks for cleaning this up.

thx!
hofrat 

Re: [tip:timers/core] time: Move timeconst.h into include/generated

[Stephen Boyd]

On 05/19/2015 06:36 AM, tip-bot for Nicholas Mc Guire wrote:
> Commit-ID:  0a227985d4a993a322ff72ecbaeee2611d624216
> Gitweb:     http://git.kernel.org/tip/0a227985d4a993a322ff72ecbaeee2611d624216
> Author:     Nicholas Mc Guire <hofrat@osadl.org>
> AuthorDate: Mon, 18 May 2015 14:19:12 +0200
> Committer:  Thomas Gleixner <tglx@linutronix.de>
> CommitDate: Tue, 19 May 2015 15:13:45 +0200
>
> time: Move timeconst.h into include/generated
>
> kernel/time/timeconst.h is moved to include/generated/ and generated 
> by the top level Kbuild. This allows using timeconst.h in an earlier
> build stage.
>
> Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
> Cc: Masahiro Yamada <yamada.m@jp.panasonic.com>
> Cc: Sam Ravnborg <sam@ravnborg.org>
> Cc: Joe Perches <joe@perches.com>
> Cc: John Stultz <john.stultz@linaro.org>
> Cc: Andrew Hunter <ahh@google.com>
> Cc: Paul Turner <pjt@google.com>
> Cc: Michal Marek <mmarek@suse.cz>
> Link: http://lkml.kernel.org/r/1431951554-5563-1-git-send-email-hofrat@osadl.org
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---

This patch seems to cause kernel/time/time.c to always need to be
recompiled and the vmlinux to be relinked even if nothing has changed.

make V=2 shows

  CC      kernel/time/time.o - due to: include/config/


> diff --git a/Kbuild b/Kbuild
> index 6f0d82a..df99a5f 100644
> --- a/Kbuild
> +++ b/Kbuild
> @@ -2,8 +2,9 @@
>  # Kbuild for top-level directory of the kernel
>  # This file takes care of the following:
>  # 1) Generate bounds.h
> -# 2) Generate asm-offsets.h (may need bounds.h)
> -# 3) Check for missing system calls
> +# 2) Generate timeconst.h
> +# 3) Generate asm-offsets.h (may need bounds.h and timeconst.h)
> +# 4) Check for missing system calls
>  
>  # Default sed regexp - multiline due to syntax constraints
>  define sed-y
> @@ -47,7 +48,26 @@ $(obj)/$(bounds-file): kernel/bounds.s FORCE
>  	$(call filechk,offsets,__LINUX_BOUNDS_H__)
>  
>  #####
> -# 2) Generate asm-offsets.h
> +# 2) Generate timeconst.h
> +
> +timeconst-file := include/generated/timeconst.h
> +
> +#always  += $(timeconst-file)

Is there a reason this is commented out instead of removed?

> +targets += $(timeconst-file)
> +
> +quiet_cmd_gentimeconst = GEN     $@
> +define cmd_gentimeconst
> [...]
> diff --git a/kernel/time/Makefile b/kernel/time/Makefile
> index 01f0312..ffc4cc3 100644
> --- a/kernel/time/Makefile
> +++ b/kernel/time/Makefile
> @@ -13,19 +13,4 @@ obj-$(CONFIG_TIMER_STATS)			+= timer_stats.o
>  obj-$(CONFIG_DEBUG_FS)				+= timekeeping_debug.o
>  obj-$(CONFIG_TEST_UDELAY)			+= test_udelay.o
>  
> -$(obj)/time.o: $(obj)/timeconst.h
> -
> -quiet_cmd_hzfile = HZFILE  $@
> -      cmd_hzfile = echo "hz=$(CONFIG_HZ)" > $@
> -
> -targets += hz.bc
> -$(obj)/hz.bc: $(objtree)/include/config/hz.h FORCE
> -	$(call if_changed,hzfile)
> -
> -quiet_cmd_bc  = BC      $@
> -      cmd_bc  = bc -q $(filter-out FORCE,$^) > $@
> -
> -targets += timeconst.h
> -$(obj)/timeconst.h: $(obj)/hz.bc $(src)/timeconst.bc FORCE
> -	$(call if_changed,bc)
> -
> +$(obj)/time.o: $(objtree)/include/config/

It looks like it has to recompile because of this dependency. Can't we
just remove this line?

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

Re: [tip:timers/core] time: Move timeconst.h into include/generated

[Nicholas Mc Guire]

On Mon, 29 Jun 2015, Stephen Boyd wrote:

> On 05/19/2015 06:36 AM, tip-bot for Nicholas Mc Guire wrote:
> > Commit-ID:  0a227985d4a993a322ff72ecbaeee2611d624216
> > Gitweb:     http://git.kernel.org/tip/0a227985d4a993a322ff72ecbaeee2611d624216
> > Author:     Nicholas Mc Guire <hofrat@osadl.org>
> > AuthorDate: Mon, 18 May 2015 14:19:12 +0200
> > Committer:  Thomas Gleixner <tglx@linutronix.de>
> > CommitDate: Tue, 19 May 2015 15:13:45 +0200
> >
> > time: Move timeconst.h into include/generated
> >
> > kernel/time/timeconst.h is moved to include/generated/ and generated 
> > by the top level Kbuild. This allows using timeconst.h in an earlier
> > build stage.
> >
> > Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
> > Cc: Masahiro Yamada <yamada.m@jp.panasonic.com>
> > Cc: Sam Ravnborg <sam@ravnborg.org>
> > Cc: Joe Perches <joe@perches.com>
> > Cc: John Stultz <john.stultz@linaro.org>
> > Cc: Andrew Hunter <ahh@google.com>
> > Cc: Paul Turner <pjt@google.com>
> > Cc: Michal Marek <mmarek@suse.cz>
> > Link: http://lkml.kernel.org/r/1431951554-5563-1-git-send-email-hofrat@osadl.org
> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> > ---
> 
> This patch seems to cause kernel/time/time.c to always need to be
> recompiled and the vmlinux to be relinked even if nothing has changed.
> 
> make V=2 shows
> 
>   CC      kernel/time/time.o - due to: include/config/
> 
> 
> > diff --git a/Kbuild b/Kbuild
> > index 6f0d82a..df99a5f 100644
> > --- a/Kbuild
> > +++ b/Kbuild
> > @@ -2,8 +2,9 @@
> >  # Kbuild for top-level directory of the kernel
> >  # This file takes care of the following:
> >  # 1) Generate bounds.h
> > -# 2) Generate asm-offsets.h (may need bounds.h)
> > -# 3) Check for missing system calls
> > +# 2) Generate timeconst.h
> > +# 3) Generate asm-offsets.h (may need bounds.h and timeconst.h)
> > +# 4) Check for missing system calls
> >  
> >  # Default sed regexp - multiline due to syntax constraints
> >  define sed-y
> > @@ -47,7 +48,26 @@ $(obj)/$(bounds-file): kernel/bounds.s FORCE
> >  	$(call filechk,offsets,__LINUX_BOUNDS_H__)
> >  
> >  #####
> > -# 2) Generate asm-offsets.h
> > +# 2) Generate timeconst.h
> > +
> > +timeconst-file := include/generated/timeconst.h
> > +
> > +#always  += $(timeconst-file)
> 
> Is there a reason this is commented out instead of removed?

negligence on my side - should have been removed

> 
> > +targets += $(timeconst-file)
> > +
> > +quiet_cmd_gentimeconst = GEN     $@
> > +define cmd_gentimeconst
> > [...]
> > diff --git a/kernel/time/Makefile b/kernel/time/Makefile
> > index 01f0312..ffc4cc3 100644
> > --- a/kernel/time/Makefile
> > +++ b/kernel/time/Makefile
> > @@ -13,19 +13,4 @@ obj-$(CONFIG_TIMER_STATS)			+= timer_stats.o
> >  obj-$(CONFIG_DEBUG_FS)				+= timekeeping_debug.o
> >  obj-$(CONFIG_TEST_UDELAY)			+= test_udelay.o
> >  
> > -$(obj)/time.o: $(obj)/timeconst.h
> > -
> > -quiet_cmd_hzfile = HZFILE  $@
> > -      cmd_hzfile = echo "hz=$(CONFIG_HZ)" > $@
> > -
> > -targets += hz.bc
> > -$(obj)/hz.bc: $(objtree)/include/config/hz.h FORCE
> > -	$(call if_changed,hzfile)
> > -
> > -quiet_cmd_bc  = BC      $@
> > -      cmd_bc  = bc -q $(filter-out FORCE,$^) > $@
> > -
> > -targets += timeconst.h
> > -$(obj)/timeconst.h: $(obj)/hz.bc $(src)/timeconst.bc FORCE
> > -	$(call if_changed,bc)
> > -
> > +$(obj)/time.o: $(objtree)/include/config/
> 
> It looks like it has to recompile because of this dependency. Can't we
> just remove this line?
>
yup - thats ok to drop as well - sorry that should have gone out 
after build testing.

thx!
hofrat