On Sat, 2009-08-29 at 18:46 +0200, Jan Engelhardt wrote:

On Sunday 2009-08-23 11:02, Balazs Scheidler wrote:

...

While looking for a place to add a new bitfield in ipv6_pinfo, I've found a 32 bit hole (in 64 bit mode) at the beginning of the struct. Since dst_cookie is used in the output fastpath, I've moved this field to fill the hole, thus decreasing the struct size on 64 bit platforms by 4 bytes.

Hm? I do not see a size reduction. pahole(1) tells me [for a base of v2.6.31-rc1-103-g644fc2c] the size is the same before and after.

you are right. I was inserting another bitfield and with that the size didn't grow. at the end the bitfield wasn't needed, but I still felt that dst_cookie should be moved to the first cacheline. it is used in the output fastpath. However since that's not necessarily worth in itself I can completely drop this patch. An updated version follows. By the way, what should be the proper procedure for posting patches that are tproxy specific but touch the core networking code? Should those go through Patrick, or should I just post them to netdev? Or just cross-post the patch series to both lists? commit 5ddc846b926be02c6cab93406d6e8adb1e3c9124 Author: Balazs Scheidler <bazsi@balabit.hu> Date: Sun Aug 30 08:52:01 2009 +0200 TProxy: move dst_cookie to the first cacheline in ipv6_pinfo While looking for a place to add a new bitfield in ipv6_pinfo, I've found a 32 bit hole (in 64 bit mode) at the beginning of the struct. Since dst_cookie is used in the output fastpath, I've moved this field to fill the hole. The original place of dst_cookie is now empty, but can become a place to add further fields to the struct. Signed-off-by: Balazs Scheidler <bazsi@balabit.hu> diff --git a/include/linux/ipv6.h b/include/linux/ipv6.h index c662efa..be4c9c6 100644 --- a/include/linux/ipv6.h +++ b/include/linux/ipv6.h @@ -285,6 +285,7 @@ struct ipv6_pinfo { struct in6_addr saddr; struct in6_addr rcv_saddr; struct in6_addr daddr; + __u32 dst_cookie; struct in6_pktinfo sticky_pktinfo; struct in6_addr *daddr_cache; #ifdef CONFIG_IPV6_SUBTREES @@ -348,7 +349,7 @@ struct ipv6_pinfo { */ __u8 tclass; - __u32 dst_cookie; + /* 32 bits hole on 64 bit platforms */ struct ipv6_mc_socklist *ipv6_mc_list; struct ipv6_ac_socklist *ipv6_ac_list;

--- p.1 2009-08-29 18:45:37.996787299 +0200 +++ p.2 2009-08-29 18:43:08.152753849 +0200 @@ -21824,10 +21824,8 @@ struct ipv6_pinfo { struct in6_addr saddr; /* 0 16 */ struct in6_addr rcv_saddr; /* 16 16 */ struct in6_addr daddr; /* 32 16 */ - struct in6_pktinfo sticky_pktinfo; /* 48 20 */ - - /* XXX 4 bytes hole, try to pack */ - + __u32 dst_cookie; /* 48 4 */ + struct in6_pktinfo sticky_pktinfo; /* 52 20 */ /* --- cacheline 1 boundary (64 bytes) was 8 bytes ago --- */ struct in6_addr * daddr_cache; /* 72 8 */ struct in6_addr * saddr_cache; /* 80 8 */ @@ -21862,7 +21860,9 @@ struct ipv6_pinfo { __u8 ipv6only:1; /* 106: 3 1 */ __u8 srcprefs:3; /* 106: 0 1 */ __u8 tclass; /* 107 1 */ - __u32 dst_cookie; /* 108 4 */ + + /* XXX 4 bytes hole, try to pack */ + struct ipv6_mc_socklist * ipv6_mc_list; /* 112 8 */ struct ipv6_ac_socklist * ipv6_ac_list; /* 120 8 */ /* --- cacheline 2 boundary (128 bytes) --- */

-- Bazsi