Messages in this thread | | | Date | Sat, 26 Jul 2008 15:21:18 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH 1/2] ftrace: single CPU tracers use CPU clock |
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* 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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