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Message-ID: <CAADnVQKJHXbhJFtibj34ZQ2HLbYUFURt0S3Ho4bX7LFf_GsPQw@mail.gmail.com>
Date: Thu, 4 Dec 2014 15:12:11 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Joe Perches <joe@...ches.com>,
Daniel Borkmann <dborkman@...hat.com>
Cc: Quentin Lambert <lambert.quentin@...il.com>,
"David S. Miller" <davem@...emloft.net>,
Alexey Kuznetsov <kuznet@....inr.ac.ru>,
James Morris <jmorris@...ei.org>,
Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
Patrick McHardy <kaber@...sh.net>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>,
"x86@...nel.org" <x86@...nel.org>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: bpf_jit_comp: Reduce is_ereg() code size
On Thu, Dec 4, 2014 at 3:00 PM, Joe Perches <joe@...ches.com> wrote:
> Use the (1 << reg) & mask trick to reduce code size.
>
> x86-64 size difference -O2 without profiling for various
> gcc versions:
>
> $ size arch/x86/net/bpf_jit_comp.o*
> text data bss dec hex filename
> 9266 4 0 9270 2436 arch/x86/net/bpf_jit_comp.o.4.4.new
> 10042 4 0 10046 273e arch/x86/net/bpf_jit_comp.o.4.4.old
> 9109 4 0 9113 2399 arch/x86/net/bpf_jit_comp.o.4.6.new
> 9717 4 0 9721 25f9 arch/x86/net/bpf_jit_comp.o.4.6.old
> 8789 4 0 8793 2259 arch/x86/net/bpf_jit_comp.o.4.7.new
> 10245 4 0 10249 2809 arch/x86/net/bpf_jit_comp.o.4.7.old
> 9671 4 0 9675 25cb arch/x86/net/bpf_jit_comp.o.4.9.new
> 10679 4 0 10683 29bb arch/x86/net/bpf_jit_comp.o.4.9.old
>
> Signed-off-by: Joe Perches <joe@...ches.com>
probably it was worth noting in comment that
reg is 4-bit value and AUX_REG==12, so it won't overflow.
Dave, it's for net-next of course.
Suggested-by: Alexei Starovoitov <ast@...mgrid.com>
Tested-by: Alexei Starovoitov <ast@...mgrid.com>
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