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SubjectRe: [RFC PATCH 00/10] x86: undwarf unwinder
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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