Messages in this thread | | | Date | Thu, 1 Jun 2017 06:58:20 -0500 | From | Josh Poimboeuf <> | Subject | Re: [RFC PATCH 00/10] x86: undwarf unwinder |
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On Thu, Jun 01, 2017 at 08:08:24AM +0200, Ingo Molnar wrote: > > * Josh Poimboeuf <jpoimboe@redhat.com> wrote: > > > Here's the contents of the undwarf.txt file which explains the 'why' in > > more detail: > > Ok, so the code quality looks pretty convincing to me - the new core 'undwarf' > unwinder code is a _lot_ more readable than any of the Dwarf based attempts > before. > > That we control the debug info generation at build time is icing on the cake to > me. > > One thing I'd like to see on the list of benefits side of the equation is a size > comparison of kernel .text, with frame pointers vs. undwarf, on 64-bit kernels.
Ok, will do a text size comparison. The only difficulty I encountered there is that the 'size' tool considers the .undwarf section to be text for some reason. So the "text" size grew considerably :-)
> Being able to generate more optimal code in the hottest code paths of the kernel > is the _real_, primary upstream kernel benefit of a different debuginfo method - > which has to be weighed against the pain of introducing a new unwinder. But this > submission does not talk about that aspect at all, which should be fixed I think.
Actually I devoted an entire one-sentence paragraph to performance in the documentation:
The simpler debuginfo format also enables the unwinder to be relatively fast, which is important for perf and lockdep.
But I'll try to highlight that a little more.
-- Josh
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