netdev - Re: [RFC PATCH 1/9] ipvs network name space aware

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Date:	Thu, 21 Oct 2010 10:01:12 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hans Schillstrom <hans.schillstrom@...csson.com>
Cc:	"paulmck@...ux.vnet.ibm.com" <paulmck@...ux.vnet.ibm.com>,
	Daniel Lezcano <daniel.lezcano@...e.fr>,
	"lvs-devel@...r.kernel.org" <lvs-devel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>,
	"horms@...ge.net.au" <horms@...ge.net.au>, "ja@....bg" <ja@....bg>,
	"wensong@...ux-vs.org" <wensong@...ux-vs.org>
Subject: Re: [RFC PATCH 1/9] ipvs network name space aware

Le jeudi 21 octobre 2010 à 09:45 +0200, Hans Schillstrom a écrit :
> I do have this (and some debuging)
> __rcu_read_lock()
> => 0xffffffff8108bcf3 <+0>:	push   %rbp
>    0xffffffff8108bcf4 <+1>:	mov    %rsp,%rbp
>    0xffffffff8108bcf7 <+4>:	nopl   0x0(%rax,%rax,1)
>    0xffffffff8108bcfc <+9>:	mov    %gs:0xb540,%rax
>    0xffffffff8108bd05 <+18>:	mov    0x108(%rax),%edx
>    0xffffffff8108bd0b <+24>:	inc    %edx
>    0xffffffff8108bd0d <+26>:	mov    %edx,0x108(%rax)
>    0xffffffff8108bd13 <+32>:	leaveq
>    0xffffffff8108bd14 <+33>:	retq
> 
> which is not that many, actually imprerssing few instructions :-)

nopl   0x0(%rax,%rax,1) is a filler because of extra instrumentation in
your kernel.

Maybe you could find out why your compiler dont use

	incl 0x108(%rax)

instead of

	mov    0x108(%rax),%edx
	inc    %edx
	mov    %edx,0x108(%rax)


So rcu_read_lock() is really _two_ instructions.

I agree with Paul with the "few" qualification... :-)



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