Messages in this thread | | | Date | Tue, 4 Nov 2008 17:43:58 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 3/3] ftrace: function tracer with irqs disabled |
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* 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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