linux-kernel - Re: [PATCH] x86: Align jump targets to 1 byte boundaries

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Message-ID: <CA+55aFyWonZVCwynECu1TgpraNnQ_K8YzHf9oPMUM3-St-QaPw@mail.gmail.com>
Date:	Mon, 13 Apr 2015 11:31:50 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Markus Trippelsdorf <markus@...ppelsdorf.de>
Cc:	Ingo Molnar <mingo@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Jason Low <jason.low2@...com>,
	Peter Zijlstra <peterz@...radead.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Aswin Chandramouleeswaran <aswin@...com>,
	LKML <linux-kernel@...r.kernel.org>,
	Borislav Petkov <bp@...en8.de>,
	Andy Lutomirski <luto@...capital.net>,
	Brian Gerst <brgerst@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] x86: Align jump targets to 1 byte boundaries

On Mon, Apr 13, 2015 at 10:26 AM, Markus Trippelsdorf
<markus@...ppelsdorf.de> wrote:
>
> I must have made a measurement mistake above, because the actual code
> size savings are roughly 5%:

Can you check against the -fno-guess-branch-probability output?

Does lto (without pgo) perhaps end up undoing a lot of the random
"branch out and back" noise?

                          Linus
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