From 8446f1d391f3d27e6bf9c43d4cbcdac0ca720417 Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Tue, 6 Sep 2005 15:16:27 -0700 Subject: [PATCH] detect soft lockups This patch adds a new kernel debug feature: CONFIG_DETECT_SOFTLOCKUP. When enabled then per-CPU watchdog threads are started, which try to run once per second. If they get delayed for more than 10 seconds then a callback from the timer interrupt detects this condition and prints out a warning message and a stack dump (once per lockup incident). The feature is otherwise non-intrusive, it doesnt try to unlock the box in any way, it only gets the debug info out, automatically, and on all CPUs affected by the lockup. Signed-off-by: Ingo Molnar Signed-off-by: Nishanth Aravamudan Signed-Off-By: Matthias Urlichs Signed-off-by: Richard Purdie Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/timer.c | 1 + 1 file changed, 1 insertion(+) (limited to 'kernel/timer.c') diff --git a/kernel/timer.c b/kernel/timer.c index 5377f40723f..1433d87f46b 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -950,6 +950,7 @@ void do_timer(struct pt_regs *regs) { jiffies_64++; update_times(); + softlockup_tick(regs); } #ifdef __ARCH_WANT_SYS_ALARM -- cgit v1.2.3 From 486d46aefe7ded0d343e306be740edd972aff740 Mon Sep 17 00:00:00 2001 From: Alex Williamson Date: Tue, 6 Sep 2005 15:17:04 -0700 Subject: [PATCH] optimize writer path in time_interpolator_get_counter() Christoph Lameter When using a time interpolator that is susceptible to jitter there's potentially contention over a cmpxchg used to prevent time from going backwards. This is unnecessary when the caller holds the xtime write seqlock as all readers will be blocked from returning until the write is complete. We can therefore allow writers to insert a new value and exit rather than fight with CPUs who only hold a reader lock. Signed-off-by: Alex Williamson Signed-off-by: Christoph Lameter Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/timer.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) (limited to 'kernel/timer.c') diff --git a/kernel/timer.c b/kernel/timer.c index 1433d87f46b..13e2b513be0 100644 --- a/kernel/timer.c +++ b/kernel/timer.c @@ -1429,7 +1429,7 @@ static inline u64 time_interpolator_get_cycles(unsigned int src) } } -static inline u64 time_interpolator_get_counter(void) +static inline u64 time_interpolator_get_counter(int writelock) { unsigned int src = time_interpolator->source; @@ -1443,6 +1443,15 @@ static inline u64 time_interpolator_get_counter(void) now = time_interpolator_get_cycles(src); if (lcycle && time_after(lcycle, now)) return lcycle; + + /* When holding the xtime write lock, there's no need + * to add the overhead of the cmpxchg. Readers are + * force to retry until the write lock is released. + */ + if (writelock) { + time_interpolator->last_cycle = now; + return now; + } /* Keep track of the last timer value returned. The use of cmpxchg here * will cause contention in an SMP environment. */ @@ -1456,7 +1465,7 @@ static inline u64 time_interpolator_get_counter(void) void time_interpolator_reset(void) { time_interpolator->offset = 0; - time_interpolator->last_counter = time_interpolator_get_counter(); + time_interpolator->last_counter = time_interpolator_get_counter(1); } #define GET_TI_NSECS(count,i) (((((count) - i->last_counter) & (i)->mask) * (i)->nsec_per_cyc) >> (i)->shift) @@ -1468,7 +1477,7 @@ unsigned long time_interpolator_get_offset(void) return 0; return time_interpolator->offset + - GET_TI_NSECS(time_interpolator_get_counter(), time_interpolator); + GET_TI_NSECS(time_interpolator_get_counter(0), time_interpolator); } #define INTERPOLATOR_ADJUST 65536 @@ -1491,7 +1500,7 @@ static void time_interpolator_update(long delta_nsec) * and the tuning logic insures that. */ - counter = time_interpolator_get_counter(); + counter = time_interpolator_get_counter(1); offset = time_interpolator->offset + GET_TI_NSECS(counter, time_interpolator); if (delta_nsec < 0 || (unsigned long) delta_nsec < offset) -- cgit v1.2.3