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Date: Mon, 05 May 2014 13:41:46 -0400 (EDT) From: David Miller <davem@...emloft.net> To: hannes@...essinduktion.org Cc: lorenzo@...gle.com, netdev@...r.kernel.org, yoshifuji@...ux-ipv6.org, david.laight@...lab.com, eric.dumazet@...il.com Subject: Re: [PATCH v6 1/2] net: ipv6: Unduplicate UDP, raw, and L2TP sendmsg From: Hannes Frederic Sowa <hannes@...essinduktion.org> Date: Mon, 05 May 2014 04:15:57 -0700 > Hi! > > On Fri, May 2, 2014, at 12:11, Lorenzo Colitti wrote: >> + >> +struct ip6_output_opts { >> + int hlimit: 9; >> + int tclass: 9; >> + int dontfrag: 2; >> + unsigned connected: 1; >> + struct ipv6_txoptions *opt; >> +}; > > I don't think the bitfields are useful, they can cause more RMW cycles > and at least on 64-bit systems the structure does not shrink in size if > you instead just use s16 and bool types because of the padding needed > for the pointer. On 32-bit it does save 4 bytes on the stack, but I > don't think it is worth it. > > If you put the pointer above the other members, newly added fields at > the bottom can eat into padding space instead of leaving padding holes > in it. Furthermore, some architectures are just going to pass this in via two registers anyways, so it doesn't save argument count in practice. I apologize, but I still don't like these changes :-/ -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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