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

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

> > > > 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

> When we used the preempt disabled version, we lost 5 million traces,
> as suppose to the irq disabled which was only 1,150 traces lost.
>
> Considering that we had 166,256,704 traces total, that 5 million is
> only 4% lost of traces. Still quite a lot. But again, this is an
> extreme, because we are tracing hackbench.

there's about 10% difference between the two hackbench results - so
the lack of 5% of the traces could make up for about half of that
overhead.

anyway, that still leaves the other 5% as the _true_ overhead of IRQ
disable.

is there some other workload that does not lose this many trace
entries, making it easier to compare irqs-off against preempt-off?

Ingo


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