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

YOSHIFUJI Hideaki / 吉藤英明 a écrit :

In article [ref] (at Fri, 21 Dec 2007 08:06:32 +0100), Eric Dumazet [off-list ref] says:

quoted

YOSHIFUJI Hideaki / 吉藤英明 a écrit :

quoted

In article [ref] (at Fri, 21 Dec 2007 07:03:58 +0100), Eric Dumazet [off-list ref] says:

quoted

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)