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SubjectRe: [PATCH 3/3] ftrace: function tracer with irqs disabled

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

> Running hackbench 3 times with the irqs disabled and 3 times with
> the preempt disabled function tracer yielded:
>
> tracing type times entries recorded
> ------------ -------- ----------------
> irq disabled 43.393 166433066
> 43.282 166172618
> 43.298 166256704
>
> preempt disabled 38.969 159871710
> 38.943 159972935
> 39.325 161056510

your numbers might be correct, but i found that hackbench is not
reliable boot-to-boot - it can easily produce 10% systematic noise or
more. (perhaps depending on how the various socket data structures
happen to be allocated)

the really conclusive way to test this would be to add a hack that
either does preempt disable or irqs disable, depending on a runtime
flag - and then observe how hackbench performance reacts to the value
of that flag.

note that preempt-disable will also produce less trace entries,
especially in very irq-rich workloads. Hence it will be "faster".

Ingo


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