[RESEND] [PATCH] Convert alpha to use arch_gettimeoffset()

[RESEND] [PATCH] Convert alpha to use arch_gettimeoffset()

[john stultz]

This patch converts alpha to use GENERIC_TIME via the arch_getoffset()
infrastructure, reducing the amount of arch specific code we need to
maintain.

I suspect the alpha arch could even be further improved to provide and
rpcc() based clocksource, but not having the hardware, I don't feel
comfortable attempting the more complicated conversion (but I'd be glad
to help if anyone else is interested).

This patch applies on top of Linus' current -git tree (2.6.31-rc3).

I've taken my best swing at converting this, but I'm not 100% confident
I got it right. My cross-compiler is now too old, so I couldn't check if
it builds. So any assistance from arch maintainers or testers to get
this merged would be great.

thanks
-john

Signed-off-by: John Stultz <johnstul@us.ibm.com>
---

 Kconfig       |    8 ++++++
 kernel/time.c |   72 +++-------------------------------------------------------
 2 files changed, 12 insertions(+), 68 deletions(-)

diff --git a/arch/alpha/Kconfig b/arch/alpha/Kconfig
index 9fb8aae..4434481 100644
--- a/arch/alpha/Kconfig
+++ b/arch/alpha/Kconfig
@@ -45,6 +45,14 @@ config GENERIC_CALIBRATE_DELAY
 	bool
 	default y
 
+config GENERIC_TIME
+	bool
+	default y
+
+config ARCH_USES_GETTIMEOFFSET
+	bool
+	default y
+
 config ZONE_DMA
 	bool
 	default y
diff --git a/arch/alpha/kernel/time.c b/arch/alpha/kernel/time.c
index b04e2cb..8f7eb6d 100644
--- a/arch/alpha/kernel/time.c
+++ b/arch/alpha/kernel/time.c
@@ -408,28 +408,17 @@ time_init(void)
  * part.  So we can't do the "find absolute time in terms of cycles" thing
  * that the other ports do.
  */
-void
-do_gettimeofday(struct timeval *tv)
+u32 arch_gettimeoffset(void)
 {
-	unsigned long flags;
-	unsigned long sec, usec, seq;
 	unsigned long delta_cycles, delta_usec, partial_tick;
 
-	do {
-		seq = read_seqbegin_irqsave(&xtime_lock, flags);
-
-		delta_cycles = rpcc() - state.last_time;
-		sec = xtime.tv_sec;
-		usec = (xtime.tv_nsec / 1000);
-		partial_tick = state.partial_tick;
-
-	} while (read_seqretry_irqrestore(&xtime_lock, seq, flags));
-
 #ifdef CONFIG_SMP
 	/* Until and unless we figure out how to get cpu cycle counters
 	   in sync and keep them there, we can't use the rpcc tricks.  */
 	delta_usec = 0;
 #else
+	delta_cycles = rpcc() - state.last_time;
+	partial_tick = state.partial_tick;
 	/*
 	 * usec = cycles * ticks_per_cycle * 2**48 * 1e6 / (2**48 * ticks)
 	 *	= cycles * (s_t_p_c) * 1e6 / (2**48 * ticks)
@@ -448,62 +437,9 @@ do_gettimeofday(struct timeval *tv)
 	delta_usec = ((delta_usec / ((1UL << (FIX_SHIFT-6-1)) * HZ)) + 1) / 2;
 #endif
 
-	usec += delta_usec;
-	if (usec >= 1000000) {
-		sec += 1;
-		usec -= 1000000;
-	}
-
-	tv->tv_sec = sec;
-	tv->tv_usec = usec;
-}
-
-EXPORT_SYMBOL(do_gettimeofday);
-
-int
-do_settimeofday(struct timespec *tv)
-{
-	time_t wtm_sec, sec = tv->tv_sec;
-	long wtm_nsec, nsec = tv->tv_nsec;
-	unsigned long delta_nsec;
-
-	if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC)
-		return -EINVAL;
-
-	write_seqlock_irq(&xtime_lock);
-
-	/* The offset that is added into time in do_gettimeofday above
-	   must be subtracted out here to keep a coherent view of the
-	   time.  Without this, a full-tick error is possible.  */
-
-#ifdef CONFIG_SMP
-	delta_nsec = 0;
-#else
-	delta_nsec = rpcc() - state.last_time;
-	delta_nsec = (delta_nsec * state.scaled_ticks_per_cycle 
-		      + state.partial_tick) * 15625;
-	delta_nsec = ((delta_nsec / ((1UL << (FIX_SHIFT-6-1)) * HZ)) + 1) / 2;
-	delta_nsec *= 1000;
-#endif
-
-	nsec -= delta_nsec;
-
-	wtm_sec  = wall_to_monotonic.tv_sec + (xtime.tv_sec - sec);
-	wtm_nsec = wall_to_monotonic.tv_nsec + (xtime.tv_nsec - nsec);
-
-	set_normalized_timespec(&xtime, sec, nsec);
-	set_normalized_timespec(&wall_to_monotonic, wtm_sec, wtm_nsec);
-
-	ntp_clear();
-
-	write_sequnlock_irq(&xtime_lock);
-	clock_was_set();
-	return 0;
+	return delta_usec * 1000;
 }
 
-EXPORT_SYMBOL(do_settimeofday);
-
-
 /*
  * In order to set the CMOS clock precisely, set_rtc_mmss has to be
  * called 500 ms after the second nowtime has started, because when

Re: [RESEND] [PATCH] Convert alpha to use arch_gettimeoffset()

[Andrew Morton]

On Thu, 16 Jul 2009 17:14:07 -0700
john stultz <johnstul@us.ibm.com> wrote:

> This patch converts alpha to use GENERIC_TIME via the arch_getoffset()
> infrastructure, reducing the amount of arch specific code we need to
> maintain.
> 
> I suspect the alpha arch could even be further improved to provide and
> rpcc() based clocksource, but not having the hardware, I don't feel
> comfortable attempting the more complicated conversion (but I'd be glad
> to help if anyone else is interested).
> 
> This patch applies on top of Linus' current -git tree (2.6.31-rc3).
> 
> I've taken my best swing at converting this, but I'm not 100% confident
> I got it right. My cross-compiler is now too old, so I couldn't check if
> it builds. So any assistance from arch maintainers or testers to get
> this merged would be great.
> 

It breaks the build:

cc1: warnings being treated as errors
arch/alpha/kernel/time.c: In function 'arch_gettimeoffset':
arch/alpha/kernel/time.c:413: warning: unused variable 'partial_tick'
arch/alpha/kernel/time.c:413: warning: unused variable 'delta_cycles'
make[1]: *** [arch/alpha/kernel/time.o] Error 1


u32 arch_gettimeoffset(void)
{
	unsigned long delta_cycles, delta_usec, partial_tick;

#ifdef CONFIG_SMP
	/* Until and unless we figure out how to get cpu cycle counters
	   in sync and keep them there, we can't use the rpcc tricks.  */
	delta_usec = 0;
#else
	delta_cycles = rpcc() - state.last_time;
	partial_tick = state.partial_tick;
	/*
	 * usec = cycles * ticks_per_cycle * 2**48 * 1e6 / (2**48 * ticks)
	 *	= cycles * (s_t_p_c) * 1e6 / (2**48 * ticks)
	 *	= cycles * (s_t_p_c) * 15625 / (2**42 * ticks)
	 *
	 * which, given a 600MHz cycle and a 1024Hz tick, has a
	 * dynamic range of about 1.7e17, which is less than the
	 * 1.8e19 in an unsigned long, so we are safe from overflow.
	 *
	 * Round, but with .5 up always, since .5 to even is harder
	 * with no clear gain.
	 */

	delta_usec = (delta_cycles * state.scaled_ticks_per_cycle 
		      + partial_tick) * 15625;
	delta_usec = ((delta_usec / ((1UL << (FIX_SHIFT-6-1)) * HZ)) + 1) / 2;
#endif

	return delta_usec * 1000;
}

I converted the CONFIG_SMP=y case into a plain old `return 0;'.  Which
means that we could turn the CONFIG_SMP=y case into a static inline,
really.

From: Andrew Morton <akpm@linux-foundation.org>

cc1: warnings being treated as errors
arch/alpha/kernel/time.c: In function 'arch_gettimeoffset':
arch/alpha/kernel/time.c:413: warning: unused variable 'partial_tick'
arch/alpha/kernel/time.c:413: warning: unused variable 'delta_cycles'
make[1]: *** [arch/alpha/kernel/time.o] Error 1

Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: John Stultz <johnstul@us.ibm.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: john stultz <johnstul@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 arch/alpha/kernel/time.c |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

--- a/arch/alpha/kernel/time.c~alpha-convert-to-use-arch_gettimeoffset-fix
+++ a/arch/alpha/kernel/time.c
@@ -410,13 +410,13 @@ time_init(void)
  */
 u32 arch_gettimeoffset(void)
 {
-	unsigned long delta_cycles, delta_usec, partial_tick;
-
 #ifdef CONFIG_SMP
 	/* Until and unless we figure out how to get cpu cycle counters
 	   in sync and keep them there, we can't use the rpcc tricks.  */
-	delta_usec = 0;
+	return 0;
 #else
+	unsigned long delta_cycles, delta_usec, partial_tick;
+
 	delta_cycles = rpcc() - state.last_time;
 	partial_tick = state.partial_tick;
 	/*
@@ -435,9 +435,8 @@ u32 arch_gettimeoffset(void)
 	delta_usec = (delta_cycles * state.scaled_ticks_per_cycle 
 		      + partial_tick) * 15625;
 	delta_usec = ((delta_usec / ((1UL << (FIX_SHIFT-6-1)) * HZ)) + 1) / 2;
-#endif
-
 	return delta_usec * 1000;
+#endif
 }
 
 /*
_