From: Ingo Molnar <mingo@kernel.org>
To: Markus Trippelsdorf <markus@trippelsdorf.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
"H. Peter Anvin" <hpa@zytor.com>,
Denys Vlasenko <dvlasenk@redhat.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Jason Low <jason.low2@hp.com>,
Peter Zijlstra <peterz@infradead.org>,
Davidlohr Bueso <dave@stgolabs.net>,
Tim Chen <tim.c.chen@linux.intel.com>,
Aswin Chandramouleeswaran <aswin@hp.com>,
LKML <linux-kernel@vger.kernel.org>,
Borislav Petkov <bp@alien8.de>,
Andy Lutomirski <luto@amacapital.net>,
Brian Gerst <brgerst@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH] x86: Align jump targets to 1 byte boundaries
Date: Tue, 14 Apr 2015 11:16:16 +0200 [thread overview]
Message-ID: <20150414091615.GA10345@gmail.com> (raw)
In-Reply-To: <20150414082346.GB398@x4>
* Markus Trippelsdorf <markus@trippelsdorf.de> wrote:
> On 2015.04.14 at 07:38 +0200, Ingo Molnar wrote:
> >
> > Just to make sure, could you please also apply the 3 alignment patches
> > attached below? There's a lot of noise from extra alignment.
>
> Here's an updated table:
>
> text data bss dec filename
> 8746230 970072 802816 10519118 ./vmlinux gcc-5 (lto)
> 9202488 978512 811008 10992008 ./vmlinux gcc-5
> 8036915 970296 802816 9810027 ./vmlinux gcc-5 (lto -fno-guess-branch-probability)
> 8593615 978512 811008 10383135 ./vmlinux gcc-5 (-fno-guess-branch-probability)
> 8202614 970072 802816 9975502 ./vmlinux gcc-5 (lto + Ingo's patch)
> 8801016 978512 811008 10590536 ./vmlinux gcc-5 (Ingo's patch)
> 8733943 952088 798720 10484751 ./vmlinux gcc-5 (lto + -malign-data=abi)
> 9186105 958320 806912 10951337 ./vmlinux gcc-5 (-malign-data=abi)
> 8190327 952088 798720 9941135 ./vmlinux gcc-5 (lto + Ingo's patch + -malign-data=abi)
> 8784633 958320 806912 10549865 ./vmlinux gcc-5 (Ingo's patch + -malign-data=abi)
>
> For the "lto + Ingo's patch + -malign-data=abi" combination there is a
> 10% text size reduction.
Lets rename "Ingo's patch" to "code_align=1". The interesting one
would be to compare:
code_align=1 + -fno-guess-branch-probability
vs.
lto + code_align=1 + -fno-guess-branch-probability
Or rather, you could try "Ingo's combo patch" further below, with and
without LTO.
I'd expect LTO to still be in the 5% reduction range.
> -malign-data is a new option for gcc-5 that controls how the
> compiler aligns variables. "abi" aligns variables according to psABI
> and give the tightest packing.
I'm not so sure about that one, our data access patterns are usually a
lot more well thought out than our code alignment (which is really
mostly compiler controlled). It also gives limited savings:
9202488 vmlinux gcc-5
9186105 vmlinux gcc-5 (-malign-data=abi)
Which is 0.1%. I've got a handful of options in that size range:
+ # Reduces vmlinux size by 0.25%:
+ KBUILD_CFLAGS += -fno-caller-saves
+
+ # Reduces vmlinux size by 1.10%:
+ KBUILD_CFLAGS += -fno-inline-small-functions
+
+ # Reduces vmlinux size by about 0.95%:
+ KBUILD_CFLAGS += -fno-tree-ch
but obviously they are more obscure and thus riskier. Find below an
updated "Ingo's combo patch". It gives more than 10% savings here on
x86 defconfig using gcc 4.9, without LTO.
Thanks,
Ingo
---------------->
arch/x86/Makefile | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 5ba2d9ce82dc..999e94685d12 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -77,10 +77,34 @@ 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)
+ #
+ # Don't guess branch probabilities, follow the code and unlikely()/likely() hints,
+ # which reduces vmlinux size by about 5.4%:
+ #
+ KBUILD_CFLAGS += -fno-guess-branch-probability
+
+ # Reduces vmlinux size by 0.25%:
+ KBUILD_CFLAGS += -fno-caller-saves
+
+ # Reduces vmlinux size by 1.10%:
+ KBUILD_CFLAGS += -fno-inline-small-functions
+
+ # Reduces vmlinux size by about 0.95%:
+ KBUILD_CFLAGS += -fno-tree-ch
+
# Use -mpreferred-stack-boundary=3 if supported.
KBUILD_CFLAGS += $(call cc-option,-mpreferred-stack-boundary=3)
next prev parent reply other threads:[~2015-04-14 9:16 UTC|newest]
Thread overview: 108+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-08 19:39 [PATCH 0/2] locking: Simplify mutex and rwsem spinning code Jason Low
2015-04-08 19:39 ` [PATCH 1/2] locking/mutex: Further refactor mutex_spin_on_owner() Jason Low
2015-04-09 9:00 ` [tip:locking/core] locking/mutex: Further simplify mutex_spin_on_owner() tip-bot for Jason Low
2015-04-08 19:39 ` [PATCH 2/2] locking/rwsem: Use a return variable in rwsem_spin_on_owner() Jason Low
2015-04-09 5:37 ` Ingo Molnar
2015-04-09 6:40 ` Jason Low
2015-04-09 7:53 ` Ingo Molnar
2015-04-09 16:47 ` Linus Torvalds
2015-04-09 17:56 ` Paul E. McKenney
2015-04-09 18:08 ` Linus Torvalds
2015-04-09 18:16 ` Linus Torvalds
2015-04-09 18:39 ` Paul E. McKenney
2015-04-10 9:00 ` [PATCH] mutex: Speed up mutex_spin_on_owner() by not taking the RCU lock Ingo Molnar
2015-04-10 9:12 ` Ingo Molnar
2015-04-10 9:21 ` [PATCH] uaccess: Add __copy_from_kernel_inatomic() primitive Ingo Molnar
2015-04-10 11:14 ` [PATCH] x86/uaccess: Implement get_kernel() Ingo Molnar
2015-04-10 11:27 ` [PATCH] mutex: Improve mutex_spin_on_owner() code generation Ingo Molnar
2015-04-10 12:08 ` [PATCH] x86: Align jump targets to 1 byte boundaries Ingo Molnar
2015-04-10 12:18 ` [PATCH] x86: Pack function addresses tightly as well Ingo Molnar
2015-04-10 12:30 ` [PATCH] x86: Pack loops " Ingo Molnar
2015-04-10 13:46 ` Borislav Petkov
2015-05-15 9:40 ` [tip:x86/asm] " tip-bot for Ingo Molnar
2015-05-17 6:03 ` [tip:x86/apic] " tip-bot for Ingo Molnar
2015-05-15 9:39 ` [tip:x86/asm] x86: Pack function addresses " tip-bot for Ingo Molnar
2015-05-15 18:36 ` Linus Torvalds
2015-05-15 20:52 ` Denys Vlasenko
2015-05-17 5:58 ` Ingo Molnar
2015-05-17 7:09 ` Ingo Molnar
2015-05-17 7:30 ` Ingo Molnar
2015-05-18 9:28 ` Denys Vlasenko
2015-05-19 21:38 ` [RFC PATCH] x86/64: Optimize the effective instruction cache footprint of kernel functions Ingo Molnar
2015-05-20 0:47 ` Linus Torvalds
2015-05-20 12:21 ` Denys Vlasenko
2015-05-21 11:36 ` Ingo Molnar
2015-05-21 11:38 ` Denys Vlasenko
2016-04-16 21:08 ` Denys Vlasenko
2015-05-20 13:09 ` Ingo Molnar
2015-05-20 11:29 ` Denys Vlasenko
2015-05-21 13:28 ` Ingo Molnar
2015-05-21 14:03 ` Ingo Molnar
2015-04-10 12:50 ` [PATCH] x86: Align jump targets to 1 byte boundaries Denys Vlasenko
2015-04-10 13:18 ` H. Peter Anvin
2015-04-10 17:54 ` Ingo Molnar
2015-04-10 18:32 ` H. Peter Anvin
2015-04-11 14:41 ` Markus Trippelsdorf
2015-04-12 10:14 ` Ingo Molnar
2015-04-13 16:23 ` Markus Trippelsdorf
2015-04-13 17:26 ` Markus Trippelsdorf
2015-04-13 18:31 ` Linus Torvalds
2015-04-13 19:09 ` Markus Trippelsdorf
2015-04-14 5:38 ` Ingo Molnar
2015-04-14 8:23 ` Markus Trippelsdorf
2015-04-14 9:16 ` Ingo Molnar [this message]
2015-04-14 11:17 ` Markus Trippelsdorf
2015-04-14 12:09 ` Ingo Molnar
2015-04-10 18:48 ` Linus Torvalds
2015-04-12 23:44 ` Maciej W. Rozycki
2015-04-10 19:23 ` Daniel Borkmann
2015-04-11 13:48 ` Markus Trippelsdorf
2015-04-10 13:19 ` Borislav Petkov
2015-04-10 13:54 ` Denys Vlasenko
2015-04-10 14:01 ` Borislav Petkov
2015-04-10 14:53 ` Denys Vlasenko
2015-04-10 15:25 ` Borislav Petkov
2015-04-10 15:48 ` Denys Vlasenko
2015-04-10 15:54 ` Borislav Petkov
2015-04-10 21:44 ` Borislav Petkov
2015-04-10 18:54 ` Linus Torvalds
2015-04-10 14:10 ` Paul E. McKenney
2015-04-11 14:28 ` Josh Triplett
2015-04-11 9:20 ` [PATCH] x86: Turn off GCC branch probability heuristics Ingo Molnar
2015-04-11 17:41 ` Linus Torvalds
2015-04-11 18:57 ` Thomas Gleixner
2015-04-11 19:35 ` Linus Torvalds
2015-04-12 5:47 ` Ingo Molnar
2015-04-12 6:20 ` Markus Trippelsdorf
2015-04-12 10:15 ` Ingo Molnar
2015-04-12 7:56 ` Mike Galbraith
2015-04-12 7:41 ` Ingo Molnar
2015-04-12 8:07 ` Ingo Molnar
2015-04-12 21:11 ` Jan Hubicka
2015-05-14 11:59 ` [PATCH] x86: Align jump targets to 1 byte boundaries Denys Vlasenko
2015-05-14 18:17 ` Ingo Molnar
2015-05-14 19:04 ` Denys Vlasenko
2015-05-14 19:44 ` Ingo Molnar
2015-05-15 15:45 ` Josh Triplett
2015-05-17 5:34 ` Ingo Molnar
2015-05-17 19:18 ` Josh Triplett
2015-05-18 6:48 ` Ingo Molnar
2015-05-15 9:39 ` [tip:x86/asm] x86: Align jump targets to 1-byte boundaries tip-bot for Ingo Molnar
2015-04-10 11:34 ` [PATCH] x86/uaccess: Implement get_kernel() Peter Zijlstra
2015-04-10 18:04 ` Ingo Molnar
2015-04-10 17:49 ` Linus Torvalds
2015-04-10 18:04 ` Ingo Molnar
2015-04-10 18:09 ` Linus Torvalds
2015-04-10 14:20 ` [PATCH] mutex: Speed up mutex_spin_on_owner() by not taking the RCU lock Paul E. McKenney
2015-04-10 17:44 ` Ingo Molnar
2015-04-10 18:05 ` Paul E. McKenney
2015-04-09 19:43 ` [PATCH 2/2] locking/rwsem: Use a return variable in rwsem_spin_on_owner() Jason Low
2015-04-09 19:58 ` Paul E. McKenney
2015-04-09 20:58 ` Jason Low
2015-04-09 21:07 ` Paul E. McKenney
2015-04-09 19:59 ` Davidlohr Bueso
2015-04-09 20:36 ` Jason Low
2015-04-10 2:43 ` Andev
2015-04-10 9:04 ` Ingo Molnar
2015-04-08 19:49 ` [PATCH 0/2] locking: Simplify mutex and rwsem spinning code Davidlohr Bueso
2015-04-08 20:10 ` Jason Low
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