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Date: Fri, 10 Apr 2015 14:18:08 +0200 From: Ingo Molnar <mingo@...nel.org> To: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Cc: Linus Torvalds <torvalds@...ux-foundation.org>, 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>, Denys Vlasenko <dvlasenk@...hat.com>, Brian Gerst <brgerst@...il.com>, "H. Peter Anvin" <hpa@...or.com>, Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra <a.p.zijlstra@...llo.nl> Subject: [PATCH] x86: Pack function addresses tightly as well * Ingo Molnar <mingo@...nel.org> wrote: > I realize that x86 CPU manufacturers recommend 16-byte jump target > alignments (it's in the Intel optimization manual), but the cost of > that is very significant: > > text data bss dec filename > 12566391 1617840 1089536 15273767 vmlinux.align.16-byte > 12224951 1617840 1089536 14932327 vmlinux.align.1-byte > > By using 1 byte jump target alignment (i.e. no alignment at all) we > get an almost 3% reduction in kernel size (!) - and a probably > similar reduction in I$ footprint. Likewise we could pack functions tightly as well via the patch below: text data bss dec filename 12566391 1617840 1089536 15273767 vmlinux.align.16-byte 12224951 1617840 1089536 14932327 vmlinux.align.1-byte 11976567 1617840 1089536 14683943 vmlinux.align.1-byte.funcs-1-byte Which brings another 2% reduction in the kernel's code size. It would be interesting to see some benchmarks with these two patches applied. Only lightly tested. Thanks, Ingo ============================> >From 773dbbfbf37df3520dd98e91972fbfdef5fe91ad Mon Sep 17 00:00:00 2001 From: Ingo Molnar <mingo@...nel.org> Date: Fri, 10 Apr 2015 14:14:29 +0200 Subject: [PATCH] x86: Pack function addresses tightly as well Not-Signed-off-by: Ingo Molnar <mingo@...nel.org> --- arch/x86/Makefile | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 0366d6b44a14..573d0c459f99 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -77,9 +77,12 @@ else KBUILD_AFLAGS += -m64 KBUILD_CFLAGS += -m64 - # Align jump targets to 1 byte, not the default 16 bytes: + # 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 + # Don't autogenerate traditional x87 instructions KBUILD_CFLAGS += $(call cc-option,-mno-80387) KBUILD_CFLAGS += $(call cc-option,-mno-fp-ret-in-387) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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