Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752020AbbEQFel (ORCPT ); Sun, 17 May 2015 01:34:41 -0400 Received: from mail-wg0-f52.google.com ([74.125.82.52]:35898 "EHLO mail-wg0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751126AbbEQFee (ORCPT ); Sun, 17 May 2015 01:34:34 -0400 Date: Sun, 17 May 2015 07:34:29 +0200 From: Ingo Molnar To: Josh Triplett Cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86: Align jump targets to 1 byte boundaries Message-ID: <20150517053429.GA17002@gmail.com> References: <20150514181707.GA21728@gmail.com> <20150515154540.GA12500@x> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150515154540.GA12500@x> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2118 Lines: 59 * Josh Triplett wrote: > On Mon, Sep 17, 2001 at 07:00:00AM +0000, Ingo Molnar wrote: > > * Denys Vlasenko wrote: > > > > What do you guys think about this? I think we should seriously > > > > consider relaxing our alignment defaults. > > > > > > Looks like nobody objected. I think it's ok to submit > > > this patch for real. > > > > Yeah, so my plan is to apply the following three changes from that > > discussion: > > > > --- tip.orig/arch/x86/Makefile > > +++ tip/arch/x86/Makefile > > -77,6 +77,15 else > > KBUILD_AFLAGS += -m64 > > KBUILD_CFLAGS += -m64 > > > > + # Pack jump targets tightly, don't align them to the default 16 bytes: > > + KBUILD_CFLAGS += -falign-jumps=1 > > + > > + # Pack functions tightly as well: > > + KBUILD_CFLAGS += -falign-functions=1 > > + > > + # Pack loops tightly as well: > > + KBUILD_CFLAGS += -falign-loops=1 > > + > > # Don't autogenerate traditional x87 instructions > > KBUILD_CFLAGS += $(call cc-option,-mno-80387) > > KBUILD_CFLAGS += $(call cc-option,-mno-fp-ret-in-387) > > It looks like the patch you applied to the tip tree only included one of > these (-falign-junmps=1), not the other two. It's three separate patches, in case there are any regressions. > Also, you've only applied these to 64-bit; could you please apply > them to both 32-bit and 64-bit, since many embedded systems aiming > for small code size use 32-bit? (Unless 32-bit already defaults to > these.) First things first - 64-bit is getting far more testing these days than 32-bit. > Have you considered including -falign-labels=1 as well? Does that > make a difference on top of the other three. So isn't the default on x86 for -falign-labels already 1? Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/