From 545a2bf742fb41f17d03486dd8a8c74ad511dec2 Mon Sep 17 00:00:00 2001 From: Cyril Bur Date: Thu, 12 Feb 2015 15:01:24 -0800 Subject: [PATCH] kernel/sched/clock.c: add another clock for use with the soft lockup watchdog When the hypervisor pauses a virtualised kernel the kernel will observe a jump in timebase, this can cause spurious messages from the softlockup detector. Whilst these messages are harmless, they are accompanied with a stack trace which causes undue concern and more problematically the stack trace in the guest has nothing to do with the observed problem and can only be misleading. Futhermore, on POWER8 this is completely avoidable with the introduction of the Virtual Time Base (VTB) register. This patch (of 2): This permits the use of arch specific clocks for which virtualised kernels can use their notion of 'running' time, not the elpased wall time which will include host execution time. Signed-off-by: Cyril Bur Cc: Michael Ellerman Cc: Andrew Jones Acked-by: Don Zickus Cc: Ingo Molnar Cc: Ulrich Obergfell Cc: chai wen Cc: Fabian Frederick Cc: Aaron Tomlin Cc: Ben Zhang Cc: Martin Schwidefsky Cc: John Stultz Cc: Thomas Gleixner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/sched.h | 1 + kernel/sched/clock.c | 13 +++++++++++++ kernel/watchdog.c | 2 +- 3 files changed, 15 insertions(+), 1 deletion(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 22ee0d5d7f8c..048b91b983ed 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2147,6 +2147,7 @@ extern unsigned long long notrace sched_clock(void); */ extern u64 cpu_clock(int cpu); extern u64 local_clock(void); +extern u64 running_clock(void); extern u64 sched_clock_cpu(int cpu); diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c index c27e4f8f4879..c0a205101c23 100644 --- a/kernel/sched/clock.c +++ b/kernel/sched/clock.c @@ -420,3 +420,16 @@ u64 local_clock(void) EXPORT_SYMBOL_GPL(cpu_clock); EXPORT_SYMBOL_GPL(local_clock); + +/* + * Running clock - returns the time that has elapsed while a guest has been + * running. + * On a guest this value should be local_clock minus the time the guest was + * suspended by the hypervisor (for any reason). + * On bare metal this function should return the same as local_clock. + * Architectures and sub-architectures can override this. + */ +u64 __weak running_clock(void) +{ + return local_clock(); +} diff --git a/kernel/watchdog.c b/kernel/watchdog.c index 70bf11815f84..3174bf8e3538 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -154,7 +154,7 @@ static int get_softlockup_thresh(void) */ static unsigned long get_timestamp(void) { - return local_clock() >> 30LL; /* 2^30 ~= 10^9 */ + return running_clock() >> 30LL; /* 2^30 ~= 10^9 */ } static void set_sample_period(void) -- 2.20.1