Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods
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- Subject: Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods
- From: "H. Peter Anvin" <hpa@xxxxxxxxx>
- Date: Mon, 15 Jun 2009 15:21:07 -0700
- Cc: Ingo Molnar <mingo@xxxxxxx>, Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, mingo@xxxxxxxxxx, paulus@xxxxxxxxx, acme@xxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, penberg@xxxxxxxxxxxxxx, vegard.nossum@xxxxxxxxx, efault@xxxxxx, jeremy@xxxxxxxx, npiggin@xxxxxxx, tglx@xxxxxxxxxxxxx, linux-tip-commits@xxxxxxxxxxxxxxx
- In-reply-to: <20090615215420.GE12919@Krystal>
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Mathieu Desnoyers wrote:
> * H. Peter Anvin (hpa@xxxxxxxxx) wrote:
>> Mathieu Desnoyers wrote:
>>> As the maintainer of the out-of-tree LTTng tracer, which hooks in the
>>> page fault handler with tracepoints, and which can build almost entirely
>>> as modules, I am very tempted to argue that having the nmi-code entirely
>>> robust wrt in-kernel page faults would be a very-nice-to-have feature.
>>>
>> I doubt that is ever going to be reliable, due to reentrancy issues.
>>
>> -hpa
>
> Do you mean the page fault handler code is no ever going to be reliable
> or the tracer code ?
>
> I spent a great deal of effort making LTTng lockless and reentrant wrt
> NMIs. It would be great if the low-level kernel exception handlers would
> do the same, therefore I would not have to isolate the tracer from the
> kernel as I currently do. Well, I would still continue to isolate the
> tracer from the kernel, but at least I would not have to spend as much
> effort controlling what exceptions and faults paths the tracer is
> executing.
>
So instead you want to core kernel to do your work for you?
-hpa
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