Messages in this thread | | | Date | Mon, 15 Jun 2009 17:54:20 -0400 | From | Mathieu Desnoyers <> | Subject | Re: [tip:perfcounters/core] perf_counter: x86: Fix call-chain support to use NMI-safe methods |
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* H. Peter Anvin (hpa@zytor.com) 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.
Mathieu
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