cputime: Optimize jiffies_to_cputime(1)

For powerpc with CONFIG_VIRT_CPU_ACCOUNTING
jiffies_to_cputime(1) is not compile time constant and run time
calculations are quite expensive. To optimize we use
precomputed value. For all other architectures is is
preprocessor definition.

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
LKML-Reference: <1248862529-6063-5-git-send-email-sgruszka@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

4 files changed, 19 insertions, 0 deletions

diff --git a/arch/ia64/include/asm/cputime.h b/arch/ia64/include/asm/cputime.h
index d20b998cb91..7fa8a859466 100644
--- a/arch/ia64/include/asm/cputime.h
+++ b/arch/ia64/include/asm/cputime.h
@@ -30,6 +30,7 @@ typedef u64 cputime_t;
 typedef u64 cputime64_t;
 
 #define cputime_zero			((cputime_t)0)
+#define cputime_one_jiffy		jiffies_to_cputime(1)
 #define cputime_max			((~((cputime_t)0) >> 1) - 1)
 #define cputime_add(__a, __b)		((__a) +  (__b))
 #define cputime_sub(__a, __b)		((__a) -  (__b))
diff --git a/arch/powerpc/include/asm/cputime.h b/arch/powerpc/include/asm/cputime.h
index f42e623030e..fa19f3fe05f 100644
--- a/arch/powerpc/include/asm/cputime.h
+++ b/arch/powerpc/include/asm/cputime.h
@@ -18,6 +18,9 @@
 
 #ifndef CONFIG_VIRT_CPU_ACCOUNTING
 #include <asm-generic/cputime.h>
+#ifdef __KERNEL__
+static inline void setup_cputime_one_jiffy(void) { }
+#endif
 #else
 
 #include <linux/types.h>
@@ -49,6 +52,11 @@ typedef u64 cputime64_t;
 #ifdef __KERNEL__
 
 /*
+ * One jiffy in timebase units computed during initialization
+ */
+extern cputime_t cputime_one_jiffy;
+
+/*
  * Convert cputime <-> jiffies
  */
 extern u64 __cputime_jiffies_factor;
@@ -89,6 +97,11 @@ static inline cputime_t jiffies_to_cputime(const unsigned long jif)
 	return ct;
 }
 
+static inline void setup_cputime_one_jiffy(void)
+{
+	cputime_one_jiffy = jiffies_to_cputime(1);
+}
+
 static inline cputime64_t jiffies64_to_cputime64(const u64 jif)
 {
 	cputime_t ct;
diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index eae4511ceea..211d7b0cd37 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -193,6 +193,8 @@ EXPORT_SYMBOL(__cputime_clockt_factor);
 DEFINE_PER_CPU(unsigned long, cputime_last_delta);
 DEFINE_PER_CPU(unsigned long, cputime_scaled_last_delta);
 
+cputime_t cputime_one_jiffy;
+
 static void calc_cputime_factors(void)
 {
 	struct div_result res;
@@ -500,6 +502,7 @@ static int __init iSeries_tb_recal(void)
 				tb_to_xs = divres.result_low;
 				vdso_data->tb_ticks_per_sec = tb_ticks_per_sec;
 				vdso_data->tb_to_xs = tb_to_xs;
+				setup_cputime_one_jiffy();
 			}
 			else {
 				printk( "Titan recalibrate: FAILED (difference > 4 percent)\n"
@@ -945,6 +948,7 @@ void __init time_init(void)
 	tb_ticks_per_usec = ppc_tb_freq / 1000000;
 	tb_to_us = mulhwu_scale_factor(ppc_tb_freq, 1000000);
 	calc_cputime_factors();
+	setup_cputime_one_jiffy();
 
 	/*
 	 * Calculate the length of each tick in ns.  It will not be
diff --git a/arch/s390/include/asm/cputime.h b/arch/s390/include/asm/cputime.h
index 7a3817a656d..24b1244aadb 100644
--- a/arch/s390/include/asm/cputime.h
+++ b/arch/s390/include/asm/cputime.h
@@ -42,6 +42,7 @@ __div(unsigned long long n, unsigned int base)
 #endif /* __s390x__ */
 
 #define cputime_zero			(0ULL)
+#define cputime_one_jiffy		jiffies_to_cputime(1)
 #define cputime_max			((~0UL >> 1) - 1)
 #define cputime_add(__a, __b)		((__a) +  (__b))
 #define cputime_sub(__a, __b)		((__a) -  (__b))