From: Joe Perches <joe@perches.com>
To: David Laight <David.Laight@ACULAB.COM>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
Quentin Lambert <lambert.quentin@gmail.com>,
"David S. Miller" <davem@davemloft.net>,
Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
James Morris <jmorris@namei.org>,
Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
Patrick McHardy <kaber@trash.net>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
"x86@kernel.org" <x86@kernel.org>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] x86: bpf_jit_comp: simplify trivial boolean return
Date: Thu, 27 Nov 2014 10:35:21 -0800 [thread overview]
Message-ID: <1417113321.4305.1.camel@perches.com> (raw)
In-Reply-To: <063D6719AE5E284EB5DD2968C1650D6D1C9FDA63@AcuExch.aculab.com>
On Thu, 2014-11-27 at 12:25 +0000, David Laight wrote:
> From: Joe Perches
> > On Wed, 2014-11-26 at 10:34 -0800, Alexei Starovoitov wrote:
> > > On Wed, Nov 26, 2014 at 10:02 AM, Joe Perches <joe@perches.com> wrote:
> > > > On Wed, 2014-11-26 at 09:23 -0800, Alexei Starovoitov wrote:
> > > >> On Wed, Nov 26, 2014 at 8:58 AM, Joe Perches <joe@perches.com> wrote:
> > > >
> > > >> > Is there any value in reordering these tests for frequency
> > > >> > or maybe using | instead of || to avoid multiple jumps?
> > > >>
> > > >> probably not. It's not a critical path.
> > > >> compiler may fuse conditions depending on values anyway.
> > > >> If it was a critical path, we could have used
> > > >> (1 << reg) & mask trick.
> > > >> I picked explicit 'return true' else 'return false' here,
> > > >> because it felt easier to read. Just a matter of taste.
> > > >
> > > > There is a size difference though: (allyesconfig)
> > > >
> > > > $ size arch/x86/net/built-in.o*
> > > > text data bss dec hex filename
> > > > 12999 1012 4336 18347 47ab arch/x86/net/built-in.o.new
> > > > 13177 1076 4592 18845 499d arch/x86/net/built-in.o.old
> > >
> > > interesting. Compiler obviously thinks that 178 byte increase
> > > with -O2 is the right trade off. Which I agree with :)
> > >
> > > If I think dropping 'inline' and using -Os will give bigger savings...
> >
> > This was allyesconfig which already uses -Os
> >
> > Using -O2, there is no difference using inline
> > or not, but the size delta with the bitmask is
> > much larger
> >
> > $ size arch/x86/net/built-in.o* (allyesconfig, but not -Os)
> > text data bss dec hex filename
> > 13410 820 3624 17854 45be arch/x86/net/built-in.o.new
> > 16130 884 4200 21214 52de arch/x86/net/built-in.o.old
> > 16130 884 4200 21214 52de arch/x86/net/built-in.o.static
>
> That is quite a big % change in the code size.
> Why the change in data?
$ objdump -t arch/x86/net/bpf_jit_comp.o.new > new
$ objdump -t arch/x86/net/bpf_jit_comp.o.old > old
$ diff -urN old new
--- old 2014-11-27 10:31:36.654373756 -0800
+++ new 2014-11-27 10:31:31.254373453 -0800
@@ -1,5 +1,5 @@
-arch/x86/net/bpf_jit_comp.o.old: file format elf64-x86-64
+arch/x86/net/bpf_jit_comp.o.new: file format elf64-x86-64
SYMBOL TABLE:
0000000000000000 l df *ABS* 0000000000000000 bpf_jit_comp.c
@@ -8,28 +8,26 @@
0000000000000000 l d .bss 0000000000000000 .bss
0000000000000000 l d .text.unlikely 0000000000000000 .text.unlikely
0000000000000000 l F .text 000000000000001f jit_fill_hole
-0000000000000098 l O .bss 0000000000000008 __gcov0.jit_fill_hole
+0000000000000060 l O .bss 0000000000000008 __gcov0.jit_fill_hole
0000000000000000 l d .rodata.str1.1 0000000000000000 .rodata.str1.1
0000000000000000 l d .rodata.str1.8 0000000000000000 .rodata.str1.8
-0000000000000020 l F .text 00000000000030a2 do_jit
-00000000000000c0 l O .bss 0000000000000b68 __gcov0.do_jit
+0000000000000020 l F .text 000000000000260b do_jit
+0000000000000080 l O .bss 0000000000000970 __gcov0.do_jit
00000000000006e0 l O .rodata 0000000000000034 reg2hex
0000000000000000 l d .rodata 0000000000000000 .rodata
-0000000000000060 l O .bss 0000000000000038 __gcov0.add_2mod
-0000000000000c28 l O .bss 0000000000000008 __gcov0.bpf_jit_compile
-0000000000000c40 l O .bss 00000000000003f0 __gcov0.bpf_int_jit_compile
+00000000000009f0 l O .bss 0000000000000008 __gcov0.bpf_jit_compile
+0000000000000a00 l O .bss 00000000000003f0 __gcov0.bpf_int_jit_compile
0000000000000040 l O .bss 0000000000000020 __gcov0.bpf_jit_dump
-0000000000001040 l O .bss 0000000000000028 __gcov0.bpf_jit_free
+0000000000000e00 l O .bss 0000000000000028 __gcov0.bpf_jit_free
0000000000000010 l O .bss 0000000000000018 __gcov0.bpf_prog_unlock_free
0000000000000000 l d .text.startup 0000000000000000 .text.startup
0000000000000000 l F .text.startup 0000000000000012 _GLOBAL__sub_I_65535_0_bpf_jit_compile
0000000000000000 l d .init_array 0000000000000000 .init_array
-0000000000000340 l O .data 0000000000000028 __gcov_.bpf_jit_free
-0000000000000260 l O .data 0000000000000028 __gcov_.bpf_int_jit_compile
-0000000000000220 l O .data 0000000000000028 __gcov_.bpf_jit_compile
-00000000000001e0 l O .data 0000000000000028 __gcov_.do_jit
-00000000000001a0 l O .data 0000000000000028 __gcov_.jit_fill_hole
-0000000000000160 l O .data 0000000000000028 __gcov_.add_2mod
+0000000000000300 l O .data 0000000000000028 __gcov_.bpf_jit_free
+0000000000000220 l O .data 0000000000000028 __gcov_.bpf_int_jit_compile
+00000000000001e0 l O .data 0000000000000028 __gcov_.bpf_jit_compile
+00000000000001a0 l O .data 0000000000000028 __gcov_.do_jit
+0000000000000160 l O .data 0000000000000028 __gcov_.jit_fill_hole
0000000000000120 l O .data 0000000000000028 __gcov_.bpf_jit_dump
00000000000000e0 l O .data 0000000000000028 __gcov_.bpf_prog_unlock_free
00000000000000a0 l O .data 0000000000000028 __gcov_.__get_order
@@ -43,17 +41,17 @@
0000000000000000 *UND* 0000000000000000 memset
0000000000000000 *UND* 0000000000000000 sk_load_half
0000000000000000 *UND* 0000000000000000 printk
+0000000000000000 *UND* 0000000000000000 sk_load_byte
+0000000000000000 *UND* 0000000000000000 sk_load_word
0000000000000000 *UND* 0000000000000000 sk_load_half_positive_offset
0000000000000000 *UND* 0000000000000000 sk_load_half_negative_offset
-0000000000000000 *UND* 0000000000000000 sk_load_word_positive_offset
-0000000000000000 *UND* 0000000000000000 sk_load_byte
0000000000000000 *UND* 0000000000000000 sk_load_byte_positive_offset
0000000000000000 *UND* 0000000000000000 sk_load_byte_negative_offset
-0000000000000000 *UND* 0000000000000000 sk_load_word
+0000000000000000 *UND* 0000000000000000 sk_load_word_positive_offset
0000000000000000 *UND* 0000000000000000 __bpf_call_base
0000000000000000 *UND* 0000000000000000 sk_load_word_negative_offset
-00000000000030d0 g F .text 0000000000000013 bpf_jit_compile
-00000000000030f0 g F .text 0000000000000352 bpf_int_jit_compile
+0000000000002630 g F .text 0000000000000013 bpf_jit_compile
+0000000000002650 g F .text 0000000000000352 bpf_int_jit_compile
0000000000000000 g O .data..read_mostly 0000000000000004 bpf_jit_enable
0000000000000000 *UND* 0000000000000000 __kmalloc
0000000000000000 *UND* 0000000000000000 bpf_jit_binary_alloc
@@ -62,7 +60,7 @@
0000000000000000 *UND* 0000000000000000 set_memory_ro
0000000000000000 *UND* 0000000000000000 kfree
0000000000000000 *UND* 0000000000000000 bpf_jit_binary_free
-0000000000003450 g F .text 000000000000008c bpf_jit_free
+00000000000029b0 g F .text 000000000000008c bpf_jit_free
0000000000000000 *UND* 0000000000000000 set_memory_rw
0000000000000000 *UND* 0000000000000000 __bpf_prog_free
0000000000000000 *UND* 0000000000000000 __gcov_init
next prev parent reply other threads:[~2014-11-27 18:35 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-26 18:34 [PATCH] x86: bpf_jit_comp: simplify trivial boolean return Alexei Starovoitov
2014-11-26 18:41 ` Joe Perches
2014-11-26 20:00 ` Joe Perches
2014-11-27 12:25 ` David Laight
2014-11-27 14:36 ` Quentin Lambert
2014-11-27 18:35 ` Joe Perches [this message]
2014-11-27 18:49 ` Joe Perches
2014-12-04 9:26 ` Joe Perches
2014-12-04 15:56 ` Alexei Starovoitov
2014-12-04 18:05 ` Joe Perches
-- strict thread matches above, loose matches on Subject: below --
2014-12-04 22:44 Alexei Starovoitov
2014-11-26 17:23 Alexei Starovoitov
2014-11-26 18:02 ` Joe Perches
2014-11-26 16:42 Alexei Starovoitov
2014-11-26 16:58 ` Joe Perches
2014-11-26 17:55 ` Daniel Borkmann
2014-11-26 9:18 Quentin Lambert
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