From: Nicolas Cavallari <nicolas.cavallari@green-communications.fr>
To: Julian Anastasov <ja@ssi.bg>
Cc: netdev@vger.kernel.org, "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>
Subject: Re: [PATCHv2] ipv4: Do not cache routing failures due to disabled forwarding.
Date: Thu, 18 Sep 2014 08:43:06 +0200 [thread overview]
Message-ID: <541A7EFA.8070506@green-communications.fr> (raw)
In-Reply-To: <alpine.LFD.2.11.1409180749570.4152@ja.home.ssi.bg>
On 18/09/2014 07:17, Julian Anastasov wrote:
>
> Hello,
>
> On Mon, 15 Sep 2014, Nicolas Cavallari wrote:
>
>> If we cache them, the kernel will reuse them, independently of
>> whether forwarding is enabled or not. Which means that if forwarding is
>> disabled on the input interface where the first routing request comes
>> from, then that unreachable result will be cached and reused for
>> other interfaces, even if forwarding is enabled on them.
>>
>> This can be verified with two interfaces A and B and an output interface
>> C, where B has forwarding enabled, but not A and trying
>> ip route get $dst iif A from $src && ip route get $dst iif B from $src
>>
>> Signed-off-by: Nicolas Cavallari <nicolas.cavallari@green-communications.fr>
>
> Looks good to me,
>
> Reviewed-by: Julian Anastasov <ja@ssi.bg>
>
> Still, I fail to see how the compiler optimizes
> the jump, 'goto local_input' still jumps to res.fi check.
> I tried even likely() after 'local_input:" checks for
> res.fi and !itag but the 'if (res.fi) {' block is still
> moved below and reached with jnz. I expected likely() to
> prefer the res.fi != NULL path.
Different compiler/arch/options perhaps ? I'm using Debian's GCC
4.9.1-11 on amd64 with a defconfig + CONFIG_DEBUG_INFO. It does this:
.LBE2727:
.loc 1 1800 0
movb $7, -102(%rbp) #, res.type
.loc 1 1801 0
movq $0, -96(%rbp) #, res.fi
xorl %ecx, %ecx # D.60248
.loc 1 1653 0
xorl %r12d, %r12d # flags
.LVL737:
.loc 1 1749 0
xorl %r15d, %r15d # do_cache
.LVL738:
jmp .L784 #
where .L784 is :
.loc 1 1762 0
movl 324(%r11), %edi # in_dev_74->cnf.data,
xorl %esi, %esi # D.60250
.LVL601:
movq %r10, -128(%rbp) # skb, %sfp
testl %edi, %edi #
movq 264(%r14), %rdi # _75->loopback_dev, _75->loopback_dev
setne %sil #, D.60250
xorl %edx, %edx #
.LVL602:
call rt_dst_alloc #
As for the res.fi and itag check in local_input, it jumps only when the
test fails.
next prev parent reply other threads:[~2014-09-18 6:43 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-13 12:59 [RFC] ipv4: Do not cache routing failures due to disabled forwarding Nicolas Cavallari
2014-09-15 10:28 ` [PATCHv2] " Nicolas Cavallari
2014-09-16 18:54 ` David Miller
2014-09-16 19:52 ` Nicolas Cavallari
2014-09-23 8:34 ` Nicolas Cavallari
2014-09-23 15:28 ` David Miller
2014-09-18 5:17 ` Julian Anastasov
2014-09-18 6:43 ` Nicolas Cavallari [this message]
2014-09-18 8:04 ` Julian Anastasov
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