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Finding a profiler that works, damnitFinding a profiler that works, damnitPosted Mar 26, 2010 21:44 UTC (Fri) by foom (subscriber, #14868)In reply to: Finding a profiler that works, damnit by sandmann Parent article: KVM, QEMU, and kernel project management
I'm probably missing something, but...
Why does it need to happen at NMI time? Why can't you just do it in the user process's context,
The setitimer(ITIMER_PROF) solution that userspace profilers use clearly works out fine for
The stack trace of the userspace half clearly can't change between when you received the NMI and
That just leaves the complication of implementing the DWARF unwinder in the kernel, but there's
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Finding a profiler that works, damnit Posted Mar 26, 2010 23:28 UTC (Fri) by nix (subscriber, #2304) [Link]
There is already a DWARF unwinder in the kernel (or was, and it could be
resurrected). The tricky part is making it paranoid enough to be non-DoSable, even by hostile generators of DWARF2. IIRC the kernel unwinder was ripped out by Linus because it kept falling over when unwinding purely kernel stack frames...
Finding a profiler that works, damnit Posted Mar 27, 2010 14:10 UTC (Sat) by garloff (subscriber, #319) [Link]
Finding a profiler that works, damnit Posted Mar 27, 2010 15:12 UTC (Sat) by foom (subscriber, #14868) [Link]
Care to expand upon that link with some explanatory text?
Finding a profiler that works, damnit Posted Mar 28, 2010 0:26 UTC (Sun) by garloff (subscriber, #319) [Link]
Sorry, that was somewhat terse. The Novell Kernel Debugger has stack
unwinding features built-in; so this is something that might be leveraged in another project.
Finding a profiler that works, damnit Posted Apr 4, 2010 12:35 UTC (Sun) by chantecode (subscriber, #54535) [Link]
We need to profile from NMI if we want to profile irqs as well. Otherwise a hardware pmu event would occur at the end of an irq disabled section, not at the exact place of the event, messing completely the result.
Finding a profiler that works, damnit Posted Apr 5, 2010 1:37 UTC (Mon) by foom (subscriber, #14868) [Link]
You need to get stack traces for the *kernel* from an NMI. Surely the userspace backtracing can
wait until a more convenient time...
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