Re: Random panic in load_balance() with 3.16-rc

From: Alexei Starovoitov
Date: Mon Jul 28 2014 - 13:27:49 EST

On Mon, Jul 28, 2014 at 09:45:45AM -0700, Linus Torvalds wrote:
> On Mon, Jul 28, 2014 at 5:26 AM, Frank Ch. Eigler <fche@xxxxxxxxxx> wrote:
> >
> > Please note that the data produced by "-g -fvar-tracking" is consumed
> > by tools like systemtap, perf, crash, and makes a significant
> > difference to the observability of debug AND non-debug kernels.
> Yeah, and compared to having a buggy kernel, I care exactly this much: "".
> Besides, "significant difference" is very debatable indeed. It may be
> noticeable, it's likely not actually significant.

as far as I can see in gcc code, -fno-var-tracking-assignments is the main
switch for 'vartrack' pass. So -fno-var-tracking-assignments is pretty
much equivalent to -fno-var-tracking
Both kill majority of debug info for local variables and function arguments.
The end effect for perf/systemtap will be quite noticeable.

It's not pretty, but adding it unconditionally was the right thing to do.
Black listing compiler versions is too fragile.
Look at the flip side: now size of build dir will be much smaller :)

For gcc it's obviously a big blow. Now 10k lines pass developed
over 10+ years will not be used :(

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