Re: [TCP] IPV6 : Change a divide into a right shift in tcp_v6_send_ack()

[Eric Dumazet <dada1@cosmosbay.com>]

YOSHIFUJI Hideaki / 吉藤英明 a écrit :
> In article <476B65F8.10201@cosmosbay.com> (at Fri, 21 Dec 2007 08:06:32 +0100), Eric Dumazet <dada1@cosmosbay.com> says:
> 
>> YOSHIFUJI Hideaki / 吉藤英明 a écrit :
>>> In article <476B574E.80601@cosmosbay.com> (at Fri, 21 Dec 2007 07:03:58 +0100), Eric Dumazet <dada1@cosmosbay.com> says:
>>>
>>>> Because tot_len is signed in tcp_v6_send_ack(), tot_len/4 forces compiler
>>>> to emit an integer divide, while we can help it to use a right shift,
>>>> less expensive.
>>> Are you really sure?
>>> At least, gcc-4.1.2-20061115 (debian) does not make any difference.
>>>
>>> And, IMHO, because shift for signed variable is fragile, so we should
>>> avoid using it.
>>>
>> Yes I am sure, but maybe you are on x86_64 ?
>>
>> gcc-4.2.2 on x86
> 
> I'm on gcc-4.1.2 20061115 (prerelease) (Debian 4.1.1-21), on x86 (i686).
> Maybe compiler difference?!

hum, more probably a .config difference. Try with

CONFIG_CC_OPTIMIZE_FOR_SIZE=Y

(default config)