Re: [BISECTION RESULT] sched: revert cpu_clock to

Peter Zijlstra
2008-08-05T08:56:25Z

On Mon, 2008-08-04 at 12:46 -0700, Nishanth Aravamudan wrote:
> Bisection on an x455 (2-node IA64) showed that commit
> 27ec4407790d075c325e1f4da0a19c56953cce23 (sched: make cpu_clock()
> globally synchronous) broke booting. I see the uncompressing initramfs
> message and then nothing on the console. I wait about 5 minutes (which
> is way longer than it takes for the first console messages to get
> printed normally). The commit immediately before it works fine.
>
> The commit no longer cleanly reverts, but I tried to manually put things
> back to the way they were before in cpu_clock(). The resulting kernel
> boots fine. I could figure out a clean way to leave cpu_clock() in
> sched_clock.c because of all the rq dependencies from sched.c. The
> attempt I tested is below [1]. This patch is *NOT* for inclusion, just
> to demonstrate what I tested.
>
> I'm happy to test any better patches.

Does this work for you?

---
Subject: sched_clock: delay using sched_clock()

Some arch's can't handle sched_clock() being called too early - delay
this until sched_clock_init() has been called.

Reported-by: Bill Gatliff <bgat@billgatliff.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Russell King - ARM Linux <linux@arm.linux.org.uk>
---
include/linux/sched.h | 14 +++-----------
kernel/sched_clock.c | 18 ++++++++++++++++--
2 files changed, 19 insertions(+), 13 deletions(-)

Index: linux-2.6/include/linux/sched.h
=================================--- linux-2.6.orig/include/linux/sched.h
+++ linux-2.6/include/linux/sched.h
@@ -1551,16 +1551,10 @@ static inline int set_cpus_allowed(struc

extern unsigned long long sched_clock(void);

-#ifndef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
-static inline void sched_clock_init(void)
-{
-}
-
-static inline u64 sched_clock_cpu(int cpu)
-{
- return sched_clock();
-}
+extern void sched_clock_init(void);
+extern u64 sched_clock_cpu(int cpu);

+#ifndef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
static inline void sched_clock_tick(void)
{
}
@@ -1584,8 +1578,6 @@ static inline void sched_clock_tick_star
#endif

#else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
-extern void sched_clock_init(void);
-extern u64 sched_clock_cpu(int cpu);
extern void sched_clock_tick(void);
extern void sched_clock_idle_sleep_event(void);
extern void sched_clock_idle_wakeup_event(u64 delta_ns);
Index: linux-2.6/kernel/sched_clock.c
=================================--- linux-2.6.orig/kernel/sched_clock.c
+++ linux-2.6/kernel/sched_clock.c
@@ -32,6 +32,7 @@
#include <linux/ktime.h>
#include <linux/module.h>

+static __read_mostly int sched_clock_running;

#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK

@@ -71,8 +72,6 @@ static inline struct sched_clock_data *c
return &per_cpu(sched_clock_data, cpu);
}

-static __read_mostly int sched_clock_running;
-
void sched_clock_init(void)
{
u64 ktime_now = ktime_to_ns(ktime_get());
@@ -319,6 +318,21 @@ void sched_clock_idle_wakeup_event(u64 d
}
EXPORT_SYMBOL_GPL(sched_clock_idle_wakeup_event);

+#else /* CONFIG_HAVE_UNSTABLE_SCHED_CLOCK */
+
+void sched_clock_init(void)
+{
+ sched_clock_running = 1;
+}
+
+u64 sched_clock_cpu(int cpu)
+{
+ if (unlikely(!sched_clock_running))
+ return 0;
+
+ return sched_clock();
+}
+
#endif

/*