Messages in this thread |  | | | Date | Tue, 16 Jun 2009 15:37:11 -0700 | | From | "H. Peter Anvin" <> | | Subject | Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods |
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Mathieu Desnoyers wrote: > > So, in summary : > > - near-zero measurable runtime cost. > - NMI-reentrancy constraint on a very small and well-defined trap > handler code path. > - simplifies life of tracer and profilers. (meaning : makes a lot of > _other_ kernel code much easier to write and understand) > - removes ad-hoc corner cases management from those users. > - provides early error detection because the nmi-reentrant code path is > shared by all users. > > So I'll use your own argument : making this trap handler code path > nmi-reentrant will simplify an already existing bunch of in-kernel users > (oprofile, perf counter tool, ftrace..). Moving the burden from > subsystems spread across the kernel tree to a single, well defined spot > looks like a constraint that will _diminish_ overall kernel development > cost. >
No, this is utter bullshit.
YOU ARE ADDING A CONSTRAINT TO ONE OF THE HOTTEST PATHS IN THE KERNEL.
Constraining future optimizations.
To support tools.
That is what I'm objecting to.
-hpa
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