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Date:   Mon, 21 Oct 2019 10:05:49 -0500
From:   Josh Poimboeuf <jpoimboe@redhat.com>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        Joe Lawrence <joe.lawrence@redhat.com>,
        Jessica Yu <jeyu@kernel.org>, Miroslav Benes <mbenes@suse.cz>,
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        bristot@redhat.com, jbaron@akamai.com,
        torvalds@linux-foundation.org, tglx@linutronix.de,
        mingo@kernel.org, namit@vmware.com, hpa@zytor.com, luto@kernel.org,
        ard.biesheuvel@linaro.org, live-patching@vger.kernel.org
Subject: Re: [PATCH v3 5/6] x86/ftrace: Use text_poke()
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On Wed, Oct 16, 2019 at 09:42:17AM +0200, Peter Zijlstra wrote:
> > which are not compatible with livepatching. GCC upstream now has
> > -flive-patching option, which disables all those interfering optimizati=
ons.
>=20
> Which, IIRC, has a significant performance impact and should thus really
> not be used...
>=20
> If distros ship that crap, I'm going to laugh at them the next time they
> want a single digit performance improvement because *important*.

I have a crazy plan to try to use objtool to detect function changes at
a binary level, which would hopefully allow us to drop this flag.

But regardless, I wonder if we enabled this flag prematurely.  We still
don't have a reasonable way to use it for creating source-based live
patches upstream, and it should really be optional for CONFIG_LIVEPATCH,
since kpatch-build doesn't need it.

--=20
Josh