Re: [PATCH] arm64: defconfig: Disable DEBUG_INFO

From: Catalin Marinas <catalin.marinas@arm.com>
To: Mark Brown <broonie@kernel.org>
Cc: Will Deacon <will@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	Guillaume Tucker <guillaume.tucker@collabora.com>,
	Kevin Hilman <khilman@baylibre.com>
Subject: Re: [PATCH] arm64: defconfig: Disable DEBUG_INFO
Date: Thu, 4 Mar 2021 16:22:32 +0000	[thread overview]
Message-ID: <20210304162231.GA29547@arm.com> (raw)
In-Reply-To: <20210304151853.GC4731@sirena.org.uk>

On Thu, Mar 04, 2021 at 03:18:53PM +0000, Mark Brown wrote:
> On Thu, Mar 04, 2021 at 02:48:34PM +0000, Will Deacon wrote:
> > On Thu, Mar 04, 2021 at 02:36:47PM +0000, Mark Brown wrote:
> > > they allocate to jobs (that's certainly what KernelCI does).  Testing
> > > modified versions of configurations isn't great as half the point of
> > > using the standard configurations is that everyone's working to the same
> > > thing and should in theory be seeing the same stuff, it's easier to name
> > > a standard config than name a standard config and a list of tweaks
> > > applied to it.
> 
> > I'd be fine if arm64 build reports came back as "defconfig+DEBUG_INFO=n"
> > and the CI just ran ./scripts/config -d DEBUG_INFO as part of its build
> > step. For runtime testing, however, having the full vmlinux available is
> > really helpful if we need to debug.

I found DEBUG_INFO pretty useful as well and always hated it in the past
when I had to recompile a kernel just to rerun the tests and identify
the source/line of an address (I guess that's why we ended up with this
in defconfig).

> > > This is about picking a sensible default, there's always going to be
> > > cases where someone wants the other value (otherwise it wouldn't be a
> > > config option).  The contention is that there's a lot more builds being
> > > slowed down by the extra I/O and disk space being burned than benefit to
> > > people who end up with the debug info turned on and actively use it but
> > > these aren't direct tradeoffs so you can't categorically say something
> > > one way or the other.  At the minute defconfig actually results in a
> > > bigger build tree than an allmodconfig for me (6.8G vs 5.2G) which
> > > doesn't seem like what I'd expect.
> 
> > I suppose I'm of the opinion that debug info is a waste of time until you
> > need it, and then it's suddenly invaluable. So I'd prefer it to be there by
> > default, as I don't think the extra I/O or disk space is a concern outside
> > of CI. But it would be good to hear what others have to say.
> 
> FWIW with laptops the I/O cost tends to make a difference to the
> edit/compile/run time for me, disks are slow and RAM not plentiful.
> Right now I'm sitting at a rather high speced desktop so the build trees
> I got the storage numbers from were all in RAM backed tmpfs and it makes
> very little odds.

How about enabling DEBUG_INFO_REDUCED as a middle ground? For me the
build tree goes from 5.9GB to 2.0GB. I tried faddr2line and still works
as expected (only tried gcc, not sure whether clang honours this
option).

-- 
Catalin

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