Messages in this thread | | | From | Chris Wilson <> | Subject | Re: [PATCH v2 1/2] trace: Default to using trace_global_clock if sched_clock is unstable | Date | Wed, 04 Apr 2018 21:46:18 +0100 |
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Quoting Chris Wilson (2018-03-30 16:01:31) > Across suspend, we may see a very large drift in timestamps if the sched > clock is unstable, prompting the global trace's ringbuffer code to warn > and suggest switching to the global clock. Preempt this request by > detecting when the sched clock is unstable (determined during > late_initcall) and automatically switching the default clock over to > trace_global_clock. > > This should prevent requiring user interaction to resolve warnings such > as: > > Delta way too big! 18446743856563626466 ts=18446744054496180323 write stamp = 197932553857 > If you just came from a suspend/resume, > please switch to the trace global clock: > echo global > /sys/kernel/debug/tracing/trace_clock > > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> > Cc: Steven Rostedt (VMware) <rostedt@goodmis.org> > --- > v2: Tell the user what's happening and what they can do to correct it. > --- > kernel/trace/trace.c | 19 +++++++++++++++++++ > 1 file changed, 19 insertions(+) > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index 13baf85b27d8..7c155fa879e1 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -41,6 +41,7 @@ > #include <linux/nmi.h> > #include <linux/fs.h> > #include <linux/trace.h> > +#include <linux/sched/clock.h> > #include <linux/sched/rt.h> > > #include "trace.h" > @@ -8505,3 +8506,21 @@ __init static int clear_boot_tracer(void) > > fs_initcall(tracer_init_tracefs); > late_initcall_sync(clear_boot_tracer); > + > +#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK > +__init static int tracing_set_default_clock(void) > +{ > + /* sched_clock_stable() is determined in late_initcall */ > + if (trace_boot_clock || sched_clock_stable()) {
Oh flip, I reversed the logic from v1.
I was going to do an early return:
if (trace_boot_clock || sched_clock_stable()) return;
to shift the message to the left slightly, at left it half way.
(I was wondering why CI didn't show the same results as v1!) -Chris
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