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authorCyril Bur <cyrilbur@gmail.com>2015-02-12 15:01:24 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2015-02-12 18:54:13 -0800
commit545a2bf742fb41f17d03486dd8a8c74ad511dec2 (patch)
treef4e73814dd6f4df296e913f2089244759eb33108 /kernel/sched/clock.c
parentdd4a5c1e6531b9c6ba6ee1f3cb11f0aeea25881e (diff)
downloadlinux-545a2bf742fb41f17d03486dd8a8c74ad511dec2.tar.bz2
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 <cyrilbur@gmail.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Andrew Jones <drjones@redhat.com> Acked-by: Don Zickus <dzickus@redhat.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Ulrich Obergfell <uobergfe@redhat.com> Cc: chai wen <chaiw.fnst@cn.fujitsu.com> Cc: Fabian Frederick <fabf@skynet.be> Cc: Aaron Tomlin <atomlin@redhat.com> Cc: Ben Zhang <benzh@chromium.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: John Stultz <john.stultz@linaro.org> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/sched/clock.c')
-rw-r--r--kernel/sched/clock.c13
1 files changed, 13 insertions, 0 deletions
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();
+}