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SubjectRe: [PATCH 1/2] ftrace: single CPU tracers use CPU clock

* Steven Rostedt <rostedt@goodmis.org> wrote:

> > this is not a good idea. We want to fix cpu_clock(), not work around
> > any deficiencies it might have.
>
> cpu_clock currently is "sched_clock" when the
> CONFIG_HAVE_UNSTABLE_SCHED_CLOCK is not set. Which is done via
> configuration, and I noticed is set on my boxes with a stable TSC??

define 'stable TSC' ;-)

> Perhaps we need to make cpu_clock change dynamically when an unstable
> sched_clock is detected.
>
> Even in this case, forcing the tracers that are single CPU to use a
> clock source that modifies itself to try to look stable across CPUs
> still seems wrong to me. The goal of looking stable across CPUs will
> always be at odds with the irqsoff tracer that does not care about
> other CPUS but cares tremendously about accurate latencies.

other tracers care too - for example to have the right chronology of
trace events. The scheduler cares too. What kind of worst-case cross-CPU
effects have you observed?

Ingo


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